Rebalancing a portfolio is difficult to swallow under the best of circumstances. Trimming what has performed well and adding to what has not runs counter to most investors' natural instincts. Moreover, the unloved asset class that you recently boosted rarely rebounds straightaway.

It has been particularly easy to ignore experts' admonitions to rebalance over the past few years. Even though many investors' equity allocations blew past their target weightings a few years ago, and stock valuations haven't looked cheap for a while, a policy of benign neglect has been not just psychologically comfortable, it has also been the winning portfolio strategy.