straights lose all the time

Two stories of flopped straights in the blind.
With seven five offsuit, I got a free play in the blind and got the perfect flop: 4, 6, 8. I checked, there was a bet and a call and I raised; the initial better re-raised, the caller folded and I went all-in and he called (I had him covered). He turned over AA -- a pre-flop raise would have gotten me to lay down my hand, so I figured he was kicking himself. An ace on the turn and a 6 on the river bailed him out for his horrible play and he took the pot with a full house.

With eight six offsuit, again in the big blind, I got a free play and was delighted by a flop of 5, 7, 9. I was in 2nd chip position with four players left in a 10 player SNG that paid three places. The player under the gun had 115 chips left; the blinds were 100/200, so he would be all in the next hand in the blind.
I checked and my opponent -- the chip leader -- bet the minimum. I raised the minimum and he called. The turn was a ten, I bet the pot and he raised; I re-raised all in and he called, turning over T,7o. The river was a seven, giving him runner-runner full house to crush my flopped straight and knock me out of the tournament in 4th place, letting my short-stacked opponent slip into the money.