That's a bit of a condescending lecture, but OK. By the way, I graduated from Brooks Institute with a degree in cinematography (yep, back in the day of film). I've shot short documentaries and also shot for a news station, and at no time did we learn to leave slop in our films. In fact, I did my lap dissolves in-camera, and the less post editing the better. That meant clean start and stop points. In documentaries I often didn't even have the option to leave "a few frames" of extra at the front.
I guess my point of confusion was that sometimes the transitions worked, and sometimes not without any definable differences in the clips (all from the same camera, the same import time, the same length clips, etc.). If there was a pattern that I could deal with I'd be fine with it. I guess I was wondering if there was something wrong with my program or the way it is loaded in the computer (I uninstalled and reinstalled, but it's still the same). I got a Mac and FCP Express because it was supposed to be "better" than what I was using on Windows. Different? Yes. Better? Not that I can see. I'm new at this program, though, so would welcome any constructive help a knowledgeable, and helpful person could offer.