"Badly" is in the eye of the beholder. Finding other mistakes on other parts of the board is helpful too, but it's important to see that if instead of connecting at H6 you play

connect at H8, white has not made too much progress with

; a 4 point reduction, perhaps. Certainly your move

was worth far more than 4 points.
Sometimes you leave weaknesses in your position by mistake, and other times you leave weaknesses in your position on purpose, because defending the weakness is too slow. Whether it's a goof or a planned sacrifice, once your opponent has made use of the weakness, you can't be unreasonable. You were able to play a move (maybe several moves) elsewhere, and profited on another part of the board; now he takes a small profit here. When you leave a real weakness
and try to keep everything, that's when disasters happen.