Misunderstood Chess Concepts

• "Don't move the same piece twice", this is a guideline, not a rule. If moving a piece twice gains significant advantage (attacking an undefended piece, seizing a critical square), do it.
• "Develop knights before bishops", usually good advice, but there are many openings where bishop development comes first (Catalan, London, etc.).
• "Castle early", excellent advice for beginners, but advanced players sometimes delay castling strategically.

• "A bishop is worth three pawns", this is a rough approximation. A bishop's value fluctuates from 2.5 to 4 pawns depending on position type. In open positions with pawns on both sides, a bishop can be worth more than a rook.
• "The bishop pair is always better", usually, but not in completely closed positions or when one bishop is bad.
• "Knights are better in closed positions", generally true, but a bishop outside the pawn chain can dominate even in closed positions.

• "Opposite-coloured bishops are drawn", in the middlegame, they actually favour the attacker. Only in pure bishop endgames do they trend toward draws.
• "Doubled pawns are weak", sometimes they're a strength (centre control, open files).
• "Rooks belong on open files", yes, but sometimes a rook is better on a closed file if it supports a pawn break.

Every chess "rule" has exceptions. The real skill is knowing when the rule applies and when it doesn't. This judgement comes from deep understanding, not memorisation. Study the principles behind the rules, not just the rules themselves. See 101 Chess Principles.