"Over analysis" here means by the opponent: If you chose the optimal move, thousands have done so before, so has your opponent. By doing something non-perfect,

"Over analysis" here means by the opponent: If you chose the optimal move, thousands have done so before, so has your opponent. By doing something non-perfect, you enter territory where your opponent does not already have the tree of possible responses mapped out in their head. This is, at least for me (a chess player), where the actual thinking begins - all before is just memorization, with the opening moves committed directly to muscle memory.