Better put, since a peak can't be predicted, is that a fund with outsize performance last year will likely underperform this year.
I remember Janus' ads running a victory lap about one fund with a >100% return in 2000, only to have ads talking about how to stay strong and deal with "uncertainty" or something after the crash.
Look at past performance of Mutual Funds. If they peaked and you buy it, you can almost be 100% sure, that it will fall.