Page "Budapest Gambit" Paragraph 28

This plan is viable only if certain conditions are met.

The d7-square must be available for the Ne5, so that it can later transfer to f6.

White should also not be able to easily advance the e3-pawn to e4, where it would be adequately defended by the Nc3 and a possible Bf3.

Finally, White should not have the time to launch a quick attack on Black's castled position with the pawn thrust f4 – f5 – f6.