To Check or Not to Check Down?

[Kapgun1]

Hello, something happened yesterday in a live MTT that I need to discuss and get a better understanding of. Here's what happened, UTG is very short stacked and raises. Everyone fold around to me, I'm in the middle position with A8o, I call, everyone else folds until the BB and he calls. Flop come K42. BB checks, at this point I do the unexplainable, I bet. My thinking was, if nobody hit that King, then I'm ahead, I felt the short stack didn't have a good hand and was only in the hand because he was the BB next hand. I'm at a point that I have half the chips that I started with, and I'm desparate to win this pot. Also, I fell I have better chances of beating one of them instead of both of them, so reduce the chance of BB sucking out on me. So it's either go home or have chips to gamble with later. Anyway the BB folds, we flip them over, short stack did indeed hit his King, I lose the hand, as the BB goes off on me. Then it got a little ugly, and the fun factor went from about 8.5 to a 2 the rest of the night, but thats a different story.

Second part of the story, I get moved to a different table and in the SB. Everyone folds until the Button and he is all-in but doesnt have enough to cover a comlete bet. I have J8o and decide to complete the bet. Then the BB raises, I fold. They flip over the cards the raiser has AJo, I think the button had small connectors. Ironically, the all-in hits a pair and takes the pot, while 4 hearts were on the board and my Jack of hearts would have won me the pot.

One of the main difference to the these two parts of the story is, one bet was made after the flop and the second part of the story the bet was made preflop.

My question is, is it ok for the guy to raise there preflop, when it wasn't OK for me to raise post flop? Also is there any circumstance at all that it's OK to raise after the flop like I did, when you didnt even hit a pair?