Trading on c3 before being asked
1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.e3 Bxc3+ 5.bxc3
- The mistake
- Playing …Bxc3+ without waiting for a3, and without a blockade in place.
- Why it costs
- White gets the two bishops for nothing and has not spent a move on a3. The doubled pawns are a weakness only if Black can attack them; traded off this early, they are simply a strong centre with c3 supporting d4.
- Instead
- Wait for a3, so the trade costs White a tempo — or keep the tension with …O-O, …d5 and …c5 and trade when the structure suits you.