Those who hold from bitcoin <$100 had confidence in it since then and that made them rich today, not all had the confidence to continue the journey , it dipped massively at some  points and  some investors sold.
Hence, it can still be cheap at the moment compare to when you start seeing it @500k .. true it's still expensive to accumulate good amount but accumulating it continously  can give you a better amount over time and how can you do that?? It's simple just practice what the thread is all about along with the DCA strategy, accumulate for cycles and check your portfolio (you will see how far you've come)