We call it 'buying the dip' but behavioral scientists have another name for it

It's called 'Escalation of commitment' or sometimes 'sunk cost fallacy' (if you ask an economist):

Escalation of commitment is a human behavior pattern in which an individual or group facing increasingly negative outcomes from a decision, action, or investment nevertheless continue the behavior instead of altering course. The actor maintains behaviors that are irrational, but align with previous decisions and actions. [wiki]

More examples: You buy a ticket for a concert and you feel sick or it's raining. You still go because you've spent money on it. You've ordered food, but you've already snacked a lot because you're so hungry. Even though you're stuffed, you're still going to eat the food you ordered because you spent so much money.

This doesn't mean that investing in bitcoin is wrong, only time will tell. However, investing in your favourite alt that's down 97% since its ATH in 2017 could turn out to be a big mistake.

Learn from 'history': look at the Top 10 of 2017. How many of them didn't you see in the last two years?

Top 20 crypto (market cap) in 2017

Just remember: there are still people investing in some of the coins you've never heard of.

Stay safe and stay rational!