I didn’t see Ng5. 😓
So, the question to ask is: What did I see? Nf6.
Why did I see Nf6?
Nf6 because I thought gxf6, Bxf6, and then Qh8 +.
But I overlooked the fact that there is a rook at f7 because my mind was kind of sticking to a familiar checkmating pattern from wishful thinking. I know the horse will be taken by the g7 pawn or the rook but I still went with it. I was lazy to find a better move.

Lesson to learn: Don’t be lazy! Don’t let your brain stick with familiar patterns. Observe all pieces and find the best move by always sticking to the principle of “Checkmate, capture, threaten.” This is an example of threaten!