Evidence made me Cry!

I actually began sobbing last nite while studying. SOBBING! I realize I am PMSing and that during times like these, AT&T commercials make me cry....but still.

I thought I understood character evidence. Apparently, I don't. I did the fucking CALI exercises for it and I scored like a 53% overall. The more I did, the more confused I got. It's like character can't come in EXCEPT EXCEPT EXCEPT EXCEPT...which ends up seeming like it gets to come in an awful lot.

The example was about entrapment -- which I know nothing about because I haven't had Crim Pro yet (is that even covered?). And when I said evidence of the defendant's prior heroin sale conviction should not be able to come in beause it seems like the prosecution was using it to show that he was selling it again. It said it COULD come in because it showed a "propensity toward selling heroin." huh? How is this different from the robbery example where evidence of a prior robbery was NOT allowed in to show that the defendant committed this one?

The answer says it's because character is part of the defense of entrapment. But I felt like that was pushing it. Is it really? As I said...now I'm just totally confused. And feel like an idiot.