[%c_effect h4;square;h4;type;GreatFind;persistent;true] The most unpleasant reaction. The pawn supports a knight jump to g5.
1. e2e4  1... e7e5  2. g1f3  2... g8f6  3. f3e5  3... d7d6  4. e5f3  4... f6e4  5. b1c3  5... e4c3  6. d2c3  6... f8e7  7. c1f4  7... e8g8  8. d1d2  8... b8d7  9. e1c1  9... d7c5 This is by far Black's most common plan. The knight is on an active square, and the light-squared bishop can soon be developed. But there's also a problem: one cannot fail to notice that the knight is far from the king now, and the monarch feels a bit insecure in a situation with castling on different flanks.