Wise investors do not live in a "world of fantasy", hoping that their coins will make them very rich in future. Always know when to take profit, not holding an altcoin for years hoping it moons over time and make you very rich. I'm not saying holding long term is wrong but from past experience, majority of coins I held long term, aside BTC and ETH didn't give me profit. Hence I sell when ever I think it's appropriate. Applying wisdom while investing is a must at this point.
Wise investors always invest in a few coins. This helps you guess with investing and not be left out of money because of one failure. I can't call myself a wise investor because I often find myself at a loss.