The personal finance rule that took me the longest to actually believe: time in the market beats timing the market.

I know the saying is a cliche. Here's the data that made it real for me.

I tracked my own 'market timing' decisions over 6 years — every time I held cash because I thought the market was overvalued or a correction was coming. In aggregate, those cash-holding periods cost me approximately 14% in returns compared to what I would have earned staying invested.

The market went up during 5 of the 7 periods I expected it to go down. The 2 times I was right, I still timed the re-entry poorly and missed a meaningful portion of the recovery.

The lesson isn't that market timing is hard — it's that market timing is harder than random chance would predict, because the factors that make investors want to hold cash (scary news, high valuations, economic uncertainty) are also the factors that have historically preceded market recoveries.