I remember of a friend who gave up his studies and went all-in on AMP coin (Synereo - if you remember the project). By saying all-in, I don't mean that he invested any money on it but all his time. He worked as a programmer for them and used to earn $300 worth of AMP each month. He did this for at least 3 years, the project did well and he almost became a double millionaire when the spike occurred in markets during 2017 when BTC was $14k and reached $20k. But he kept the coins as it is, didn't sell them when I even advised him to do so and later when the crash happened, the project itself came to an end putting all his work and savings under the grave. So, you need to know when to sell as that's too an important part of trading.
ouch so many similar stories! The hardest part is to sell when everyone is in the euphoria stage it seems like it's going to go up forever. Greed takes over I remember checking my blockfolio every 30 minutes and it just kept going up for weeks I thought I was the smartest investor ever 
then the rug pull came then I though it's just a dip then eventually I cashed out with nice gains but nowhere near the top! if I would have stayed married to the alts I would be down 95% or more. When all my nocoiner friends started buying litecoin and ripple that was the sell signal 