My son has been potty-training for about a month or so, with pretty good results. It started with a few days of wearing underwear instead of a diaper, and having accidents, since he didn't know how to go on the toilet, even though he was pretty good at holding it in.
The big breakthrough came when he learned how to go on the toilet, and since then he's been pretty good, with accidents now and then.
One of the first things he learned was to "stay dry" — in other words, no poop or pee in his pants.
However, this has led to an interesting dilemma for him — he thinks he can "stay dry" forever to avoid ever pooping or peeing. Lately, he has been expressing just how much he hates pooping and peeing. He will tell us he "has wees" and then run to the toilet, but when he gets there, he changes his mind and gets very upset - saying "No wees! Stay dry!" (He wants to try to stay dry and not ever do wees again.)
How do we teach him that staying dry is important, but that he has to go when he feels the urge and that's ok? This has led to a couple accidents, because he believes that he can stay dry, but then leaves it too long.
He usually does tell us when he gets the first urge, but then when he changes his mind, we don't like having to fight to force him to sit on the toilet at that moment (though, when we have, once he is on the toilet he will go just fine - it's just the anxiety of expectations that seem to be getting to him). I feel like a fight to sit on the toilet is a bad thing to associate with something he should be willing to do.