Bad Beat Thread

$20 limit multi table. 156 players 33 remaining. dealt AA blinds are $100-$200 I am small Blind, i raise to $600 all but 1 fold. He stays on 7 8 off suit!!!!!!!!!! the flop comes down 7 9 4, I go All-in $3500, he calls. 4th street 8 the river 7.... i lose! too often this happens, what did I do wrong?