I am starting trading some month ago.Bought some alta coin but now all alta coin are down and i donot understad what can i do?I get a big lose if i sell this.So how control my mind ? 
If you are seeing the price of the alt coin you hold are getting low better to stay away from your computer or avoid checking the charts. This is the technique that I do for most of the time especially when the price of bitcoin is getting lower. I used to check it on a daily basis but I hate to do it when the price is getting lower. You don't have to control your mind, we are there in the same situation but you have to do something about it. Go outside take time to relax.
It's better not to find out the cause because if you found it out that you are affected by that reason that may bring doom to the way you think and it will really give you a big chance of panicking or having troubles with the alt coins you are holding. Everyone should do this and it may be effective to you and others but there will people that will come out and will say that this isn't effective to them.