The most common mistake in chess is the neglect of piece development in the opening. It can happen when a player goes for material gain at the expense of speedy deployment of his forces. This nice miniature is a case in point.
It's from the African Championship in Cairo, where Egyptian GMs Bassem Amin and Ahmed Adly shared victory, both scoring 7pts in 9 games.
Abdelnabbi - Adly
1.d4 Nf6 2.c4 e6
3.Nc3 Bb4 4.Qc2
This is the Capablanca Variation. The great Cuban did not like doubled pawns and so in this line White preserves the integrity of his pawn structure, but sometimes falls behind in development.
5.dxc5 Na6 6.a3 Bxc3+
7.Qxc3 Nxc5 8.b4 Nce4
9.Qd4 d5 10.cxd5
The main line is 10.c5, but currently Black is doing well in the tactical complications arising after 10...b6 11.f3 bxc5 12.bxc5 Qa5+ 13.Qb4 Qc7 14.fxe4 Rb8 15.Qa4+ Bd7 16.c6 Qe5 17.cxd7+ Ke7.
When reaching this position, most players went for this natural move, which is in fact a very serious mistake. It was better to play 11.f3 Nd6 12.dxe6 Bxe6 13.e4, with mutual chances.
Of course, White could not snatch the e-pawn as 12.Qxe5? Nxf2! would be disastrous.
13.h3? Qb6 14.e3 (D)
White's kingside is frozen, so Black rightly went for the kill:
15.Kxf2 Ne4+ 16.Ke2 Rac8
17.Qb3 Ng3+ 18.Kf3 Nxh1
19.g4 Bc2 0-1