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

I am very sad

It seems that you are totally newbie ( by rank and also by knowledge ) because the down in the price and also up in the price of the Bitcoin is a normal things .
Here the most of the people are using the better timing to buy and sell coins and making profit .
Currently the most of the people are selling btc because of the risk to loss during the hardfork .
This is the reality that many of the newbies are feeling panic and selling Thier btc in bulk .
Here I will request you that don't keep your attention at the price of the Bitcoin and altcoins .
If you are thinking that you can make big kiss then it will be more better for you to pause your
Work for the Bitcoin field .
Here for such things I already told , visit at the
link