In his book “Secrets of Practical Chess”, John Nunn coined the phrase “Loose Pieces Drop Off”. Here is a little example that I think illustrates this rule well:
cerassee – DDT3000, ICC, 15 minutes per game
Black to Move.
White just played 21. Ba5? and seemingly created a threat to the rook on d8. However making aggressive moves before finishing development (White’s rooks have not moved yet!) is dangerous, and Black was able to exploit exactly that. As a hint – consider that Bd3 is attacked by the rook from d8, the knight on c4 is already attacked by Be6. Now also Ba5 is unprotected. Black should be able to exploit all this “looseness” of White pieces and he did… How?