This strategy is called reversion to the mean (mean reversion). The point is that most of the time the price of an asset (usually stocks and commodities) returns to its mean value (over the years) in due course
Yeah, that is probably true for stable values like world currencies or gold, oil and such. Though it would mean a really long term investment which most people that speak about trading here will never consider. At least for daytrading it is deadly... it broke my neck last time I tried my next run of learning how to trade.
Of course I traded with leverage because I only wanted to risk $20 in total for that run. It's still way way better than risking more until I can be very very sure that I have a proper advantage and loss management.