"Buying on the Dips in Your Strategy"

[F]or a strategy with long-term positive expectancy, the appropriate response to a drawdown is to increase exposure – not reduce or eliminate it – on the view that the performance of the strategy will revert to its mean.

A strategy that has performed well over the long run should never be abandoned after a decline unless there is overwhelming evidence that something about markets or the strategy has changed so fundamentally that the strategy will never work again.