#1 and #3 are easy. Guys hit you with massive raises - especially check-raises - on the flop or turn, they generally have the goods. Must fold situations. #2 is a little trickier, but look at it carefully. You bet out on a board of 8TT rainbow. What is he likely to have that he might call with - either for a draw or on a slowplay? The possibilities: any ten, pocket eights, JQ, J9, JJ, QQ, KK. The first two have you in horrible shape from the outset. The third has you in bad shape after the turn card. After you check and he bets a modest amount on the turn, don't raise - call or fold. Check to him again on the river and look for the cheapest possible showdown. This board is an ill wind blowing you no good, and all you want to do is minimize the damage. If it turns out he's an idiot who was calling you down with overcards or something, you can be happy to win a smaller pot.