Sin!

Most people would say that sin is when you do something that your not supposed to or don't do something that you are supposed to do. The big question is, "Who decides what's right and what's wrong?" Any Christian will tell you that God does and this would be correct.

My big issue is not with who decides what's right and wrong (that's obvious), but I would venture to say that the above defenition of sin is incomplete. Let me just use an example situation.

Billy wants to go hang out with his friends. As far as he knows, he isn't allowed to but he goes anyway.
Now. If he was mistaken and he is actually allowed to go hang out, has he sinned? I mean, he was allowed to go right?

These verses would seem to shed some light on the matter.
Rom.14:22-23
" 22So whatever you believe about these things keep between yourself and God. Blessed is the man who does not condemn himself by what he approves. 23But the man who has doubts is condemned if he eats, because his eating is not from faith; and everything that does not come from faith is sin."
James 4:17
"17Anyone, then, who knows the good he ought to do and doesn't do it, sins."

It would seem clear then that sin can be as much an attitude as it is an action.