Sure, that's a good plan for people who want to play in the safe zone. However, most investors are in the crypto market to get rich quickly. 20% might seem good for people who are doing this on the side, but others' plan is, the greater the risk, the better the reward. And cryptocurrencies don't just reach 95%+ profits, in the long run, 1,000%, 5,000% or even 10,000% are not strange to the crypto scene.
Seeing a 20% is sure an overwhelming feeling in the cryptomarket it is a success for a trader but then again it is not always like that way especially now its hard to see a 20% on a coin price increase because of bearish market. Being greedy may come into an end for you as a investor or trader why? because of too much speculation and expectation to a coin which is wrong, just think of bitcoin with a thousands of investor when it pumps almost 90% would sell their bitcoin obviously and will end to a massive bitcoin deflation.