That question might need slightly clarifying.
Are we talking Person A is involved in an accident caused by Person B and we are assuming to be Person B in the first part; and for the second part we are Person C who is a friend to Person A?
Or are we assuming we are Person A who is responsible for causing an accident to some unimportant person*; or Person C who is a friend to Person A who is suffering as a result of causing an accident to the unimportant person.
Note: I am not in any way endorsing that a person involved in an accident is unimportant; they just aren't for the purpose of this question.
In either scenario, though, and in a not at all selfish manner, whichever side we're on we haven't been in an accident, so we aren't in any harm. So that's good. As for which I'd rather be, I'd have to go for Person C, the one who is a friend. Whilst I can give support, I'm still living my life pretty normally and not injured/dead/comatose/guilty/remorseful etc.
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I don't know what's already been put (and I'm not looking), so:
Would you rather be unhappy knowing the truth, or being happy with a lie?
*You should assume this is about something of great importance to you.