“Why Can I Do Difficult Things but Struggle With Simple Ones?” Understanding Inconsistent Performance in ADHD

One of the most confusing experiences for many people with ADHD is inconsistency.

You might be able to spend hours solving a complicated problem at work, become remarkably knowledgeable about a subject that interests you, or organise an entire event at short notice. Yet the same person may repeatedly forget to reply to a simple email, struggle to put away the washing or spend half an hour trying to persuade themselves to make a five-minute phone call.

From the outside, this can be difficult to understand. If you can concentrate for hours on something complicated, surely you can concentrate for ten minutes on something simple?

For people with ADHD, however, difficulty is not always the thing that determines whether a task gets done.

ADHD Is Not Simply a Lack of Attention

The name “attention deficit hyperactivity disorder” can give the impression that ADHD means having too little attention. In practice, attention in ADHD is often better understood as being difficult to regulate.

Someone may struggle enormously to concentrate during a routine meeting but become completely absorbed in another activity later that day. This intense absorption is sometimes described as “hyperfocus”. Although this is not a formal diagnostic symptom, it is a useful description of an experience many people with ADHD recognise.

This can understandably cause confusion. A child who cannot remain focused on their homework might spend hours building something complicated. An adult who repeatedly misses administrative deadlines may perform exceptionally well when dealing with an urgent problem at work.

The issue is not necessarily whether they can concentrate. It is whether they can reliably direct and sustain their attention where it needs to go.

Why Interesting Things Can Feel Easier

Our brains do not respond equally to every task. Motivation, reward, novelty, urgency and personal interest all influence how readily we engage with something.

This can be particularly important in ADHD.

A task that is new, stimulating, challenging or personally meaningful may capture attention relatively easily. A repetitive or predictable task may require much more deliberate effort to begin and sustain.

This helps explain an apparent contradiction I often encounter when discussing ADHD: someone may be very capable academically or professionally while their everyday organisation feels chaotic.

Writing a complex piece of software might be interesting. Completing the accompanying expenses form may not be.

Teaching a class may provide constant stimulation and interaction. Completing the paperwork afterwards may feel disproportionately difficult.

Planning an elaborate birthday celebration might be exciting. Remembering to book a routine dental appointment can remain on a to-do list for six months.

The simpler task is not intellectually harder. It may simply provide much less stimulation.

The Problem of Getting Started

For many people with ADHD, the greatest difficulty occurs before the task has even begun.

They know what needs doing. They may genuinely intend to do it. They may even be sitting there thinking about the fact that they should be doing it.

But starting feels strangely difficult.

This is sometimes mistaken for laziness or a lack of motivation. In reality, ADHD can affect executive functions: the mental processes involved in organising behaviour, prioritising tasks, holding information in mind and moving from intention to action.

This creates the frustrating experience of wanting to do something without reliably being able to translate that intention into action at the appropriate moment.

Importantly, telling someone to “just get on with it” does not necessarily solve this problem. They probably already know that getting on with it would help.

Urgency Can Change Everything

There is another familiar ADHD pattern. A task may remain untouched for three weeks and then suddenly get completed remarkably quickly the evening before the deadline.

This can make procrastination particularly confusing.

It may look as though the person was capable of doing the task all along and simply chose not to. But the approaching deadline has changed the psychological environment. The task now has immediacy, consequences and urgency. Those factors can make it much easier to engage attention.

University assignments are a classic example. Someone might struggle to write anything for several weeks, despite repeatedly trying, before producing thousands of words in an intense burst shortly before the deadline.

The problem is that repeatedly relying on urgency comes at a cost. Working in this way can create stress, disrupted sleep and a constant sense of crisis.

“But You Managed It Yesterday”

Inconsistency can also affect how ADHD is perceived by other people.

Parents may understandably wonder why their child completed their homework independently on Monday but appears unable to do the same thing on Tuesday. Partners may become frustrated when household tasks are completed enthusiastically for several days and then forgotten. Employers may see periods of exceptional productivity alongside missed routine deadlines.

Those frustrations can be legitimate. Understanding ADHD does not mean that the consequences for other people cease to matter.

However, interpreting inconsistency as proof that someone “could do it if they really wanted to” can be unhelpful. Performance in ADHD is often influenced heavily by context: interest, fatigue, distraction, emotional state, novelty, structure, reward and urgency can all alter how manageable a task feels.

Capacity on one occasion does not necessarily mean that the same performance can be reproduced reliably in every situation.

The Effect on Self-Esteem

Years of inconsistent performance can shape how people think about themselves.

Someone may grow up repeatedly hearing that they are bright but lazy, capable but careless, or that they are “not reaching their potential”. Adults may look at their own achievements and wonder why they can cope with responsibilities that appear objectively difficult while repeatedly struggling with basic administration, housework or organisation.

Eventually, the explanation can become personal: There must be something wrong with my character.

This is one reason understanding ADHD can be so important. A diagnosis should not become an excuse for every difficulty, but it can provide a more accurate framework for understanding why certain patterns keep occurring.

Instead of asking, “Why am I so lazy?”, a more useful question might be, “What is making this particular task difficult to engage with, and what could make it easier to start?”

That change in question matters.

Working With the ADHD Brain

Recognising this pattern can also change how difficulties are approached.

If a task is repeatedly being avoided, simply applying more pressure may not be the most effective solution. Sometimes the task needs more structure. A vague instruction such as “sort out the house” may feel overwhelming, whereas one clearly defined action provides an obvious starting point.

External accountability can help some people. So can breaking a task into smaller stages, reducing distractions, working alongside another person, using visible reminders or creating an artificial deadline before the real one.

The aim is not to make every activity exciting. Real life contains plenty of boring tasks. Instead, it is about recognising that relying entirely on willpower may be unreliable and finding ways to provide the structure that the task itself does not provide.

For people receiving ADHD treatment, medication can also improve the ability to regulate attention and translate intentions into actions, although it does not remove the need for strategies, routines and realistic expectations.

A Final Thought

One of the most important things to understand about ADHD is that ability and consistency are not the same thing.

A person can be intelligent, motivated and capable while still finding apparently straightforward tasks disproportionately difficult. They may perform brilliantly when something is interesting or urgent and struggle when it is repetitive, distant or poorly defined.

That inconsistency can be frustrating for the person with ADHD and for the people around them. Understanding what lies behind it does not mean ignoring responsibility or the impact on others.

It does, however, allow us to replace an unhelpful question — “Why don't you just try harder?” — with a much more useful one:

“What would make it easier for you to get started?”

Dr James Glass
MBChB MRCPsych
Medical Director, WMI Psychiatry