Blunders I have known

 

In this position, from the game https://lichess.org/FmzpourH/black , black took the bishop and fell apart soon after... but 27...Qh5! is the move, with threats to take the Bishop, but also Bxh2+.

If after  Bh2+ if Kf1 then Qd1#

 

 

Here I played Bb2? but I had Bxg6 and then b5, 

removing both guards of the black bishop on e7. I went on to draw. https://lichess.org/Dab2BPjP/white#22