It's playable until 4...Nxe4.
piece gone = game gone
Switch off your engine and switch on your brain.
The point of no return
Sort:
Black doesn't lose his knight from 4... Nxe4, he loses it from 5... d5
Why not 5... Be6? It allows the retreat of the knight, ends the pin, and develops a piece. My brain is most definitely on 
Where is the point where black begins to have no chance of winning?
Which mistake leads to blacks' downfall? I'm pretty sure this is a playable game, until 19... Nc6
The best lines are from Rybka.