It looks like all altcoins dump 10-20%. What is the reason?

I am very sad

The reasons are varied. But what is most important to know is that you shouldn't be feeling sad at all. Dumping and pumping are two very elementary things that happen here in the world of crypto. There's fluctuation that happens no end. So, sit back and keep calm. After it falls, it rises. That's certain.

yes do not expect the market rise always that's unrealistic, you are bearing the risk and profit when you join the market , so it is very normal ,
as this guy said , just clam down and hold your coin