Concept
Rebalancing
3 books in the library reach for this idea - each in its own way. When independent authors converge on one concept, it usually deserves attention.
A Wealth of Common Sense
How this book uses it: Periodically returning to target allocation. Forces discipline by selling high and buying low.
The Bogleheads' Guide to Investing
How this book uses it: Periodically returning to your target allocation. Forces buying low and selling high.
The Four Pillars of Investing
How this book uses it: Periodically returning to your target allocation forces you to buy low and sell high - systematically.