Your investments have been doing their job, perhaps a little too enthusiastically. Stocks climbed, one fund outperformed everything else, and your retirement account now looks noticeably different from the portfolio you originally chose. Then your financial advisor recommends rebalancing.
It sounds like someone wants to rearrange your money for the sake of tidiness. There is actually a good reason behind the suggestion. Portfolio rebalancing brings your investments back toward the mix you originally selected, often by trimming assets that grew too large and adding to those that fell behind.