A man is led by two others into a cell. They leave him there and lock the door, taking the key with them.
A man goes into a room, carrying a book. He locks the door behind him and puts the key on the table. Then he sits down, facing the open window, and starts reading.
The first man's mobile phone rings. "Yes, I realise that it is important." He looks at the door. "But I can't come."
The second man's phone rings. "Yes, I realise that it is important." He looks at his book. " But, I'm sorry, I can't come."
The operative word is "choose". If there is choice there is freedom to choose.
Can and can't have nothing to do with it.
If there is freedom to choose, you choose what you want. (Even if you choose to do your duty, it is because that is what you want to do).
If you choose to can't, it is because you don't want to can. So why not say, "I don't want to"?
In order to avoid accepting responsibility. It is part of the psychological culture of blame.
NEW PROJECT: CHOOSING TO MUST.