A: 'Jim crashed his car last night. He's dead!' [or if you prefer: 'he'll spend the rest of his life in a wheelchair!']
B: The way he drives, I'm not surprised!
In this situation (everybody, including B, knows very well that Jim is a reckless driver, a danger to himself and others) doesn't, or didn't, B have a duty to try and get Jim to drive less recklessly? To point out the risks of his behaviour to him?
Of course, B didn't; any more than you or I do, when it comes to our friends. Perhaps we say 'it's their business, not mine', but I wonder how that isn't an abdication of responsibility. In fact, when quizzed, B says: 'I didn't because I knew it would be no good. He would have ignored anything I said.' The problem with this is that this describes a situation in which B would lose nothing by making his case; and since he would lose nothing, he has no grounds for shirking his duty.
You challenge B. You say: 'I tell you what I think your reason was. You didn't want to be the sort of person who goes up to a man in a wheelchair and says, I told you so!'
More to the point, nobody wants to be the sort of person who derives personal satisfaction from telling a wheelchairbound man 'I told you so!' But it's worth pondering why? What is so deplorable about this? Before the accident you look like a busybody, and after the accident you look like a gloater. But why? Is it (in the latter case) because it's too late? A reasonable objection to this is: but I told him before it was too late, hence the "I told you so"!' It does not seem to me out of the question that a more general climate of 'I told you so!' would apply pressure upon (other) people's pre-accident behaviour?