Bitcoin is a very atypical asset. Most returns are concentrated in a few days. Miss them and you may never catch up.
Here be Dragons: Bitcoin isn’t a Gaussian asset. Its returns are fat-tailed (to the right), volatility comes in regimes, and price moves are prone to discontinuities. Much of the risk is concentrated in short, nonlinear bursts rather than distributed smoothly through time. This is typical for assets still in their early price discovery stages (yes, it's early).
TL;DR: Years of pain. Days of glory.
HODLing bitcoin is an exercise of patience.