The word gets used so loosely that it has almost stopped meaning anything. A company announces accountability after a scandal and means someone was fired. A parent demands accountability and means an apology. A court orders it and means supervision. None of those are wrong exactly, but none of them are the thing itself.
Accountability is doing what you said, especially when it costs you.
That is the whole definition. Everything else is commentary.
What it is not
It is not guilt. Guilt is a feeling about the past. Accountability is a behaviour in the present. A person can feel terrible about missing work for a week and still not call their manager. The feeling is not the practice.
It is not consequences. Consequences happen to you. Accountability is something you do. When a consequence lands and you say "this is what my choice cost," that sentence is the accountable part. The cost itself was just weather.
It is not confession. Saying the hard thing out loud is a start, and it matters. But an account that stops at the admission is only half of one. The other half is what changes on Monday.
It is not self-punishment. Somewhere along the way accountability got tangled up with being hard on yourself. They are close to opposites. Contempt makes people hide. Nobody keeps a promise better because they hate themselves more.
The part that costs
The qualifier is doing the work in that definition: especially when it costs you. Keeping your word when it is easy is not a skill. Anyone returns the call they wanted to make.
The practice only shows up at the point of friction. You said you would be there at eight and you are tired. You said you would tell them the truth and the truth makes you look bad. You said you would finish it and nobody would ever know if you did not.
That gap, between what you said and what you now feel like doing, is the only place accountability exists. Which is why it cannot be taught in the abstract. It has to be practised somewhere the cost is real and somebody is watching.
Why it has to be witnessed
A commitment made only to yourself is easy to renegotiate. You are, after all, the only party at the table, and you know exactly how tired you are.
This is not a character flaw. It is how the thing works. Which is why every serious version of this practice involves saying the commitment out loud to someone who will ask about it later. Not to create pressure or shame. To create a record that does not move when your mood does.
The asking matters more than the answer. A person who is asked every week whether they did what they said will start to notice, at the moment of choice, that the question is coming.
Where it starts
Small, and out loud.
Not a resolution and not a plan for the year. One specific thing, said to one specific person, that can be answered for by Friday. Show up on time. Make the call you have been avoiding. Finish the thing that is ninety percent done.
Then answer for it. Kept or not kept, say which. The not-kept weeks teach more than the kept ones, provided nobody in the room turns them into a verdict on the person.
That is the practice. It is unglamorous, it is repetitive, and it is the only version that has ever held.