Underperformance: is it a capability issue or a conduct issue — and why does it matter?

The answer Just Ask, HR gives

Detailed Dan — Structured and thorough — every step in order.

The distinction is the whole game, because it dictates the process, the tone, and what a tribunal expects of you:

Capability = can't. They're trying, but skill, aptitude or health means the standard isn't being met. The fair response is support: clear standards, training, a realistic improvement period, reviews — a Performance Improvement Plan in plain clothes. Dismissal is fair only after genuine support has failed, with warnings along the way (typically two formal stages before dismissal for most SMEs).

Conduct = won't. They can meet the standard but choose not to — ignoring instructions, skipping tasks, carelessness born of indifference. That's the disciplinary route under the ACAS Code: investigation, hearing, warnings, potential dismissal.

Your scenario is genuinely mixed, which is common. Handle it like this:

1. Split the strands explicitly. Error-strewn reports despite training → capability. Deliberately ignoring parts of the role → conduct. Name them separately in writing; don't blur them into one vague "performance" allegation.
2. Diagnose the "can't" honestly. Was the training real? Is the workload achievable? Any health or neurodiversity angle (dyslexia and ADHD frequently sit behind "careless errors" — and may require reasonable adjustments before any formal process)?
3. Run capability with structure: specific measurable standards, a 4–12 week improvement period proportionate to the role, weekly check-ins, written outcomes at each review.
4. Run conduct through the disciplinary procedure — it can move faster than the capability track.

Why the precision matters: dismissing a "can't" case through a fast conduct process is a classic unfair dismissal. The label you choose on day one decides how defensible day ninety is.