From my own experiences, you should divide your capitals into 3 parts, one for long-term investment into a crypto that has a clear and bright future; another for surfing; and the last one as backup money for an unexpected situation.
What the author mentioned in this statement is the same with my strategy in trading or investment. But instead of dividing my capital in 3 parts I am dividing my capital into 4 to 6 parts. In my experience this kind of strategy is really effective and is useful during the price drop of bitcoins since if the value continuously goes down you will still have the resources to buy more in the most cheapest value in the market.