Sending All Monero Out?????

Today, Monero just went crazy. It almost went up 100%, so I tried to take some profit from it. I tended to send out half of my possession to exchange, however, it sent out all of them by itself. And then I checked the exchange. Only half of my Monero coins were there. I was freaked out. I did some research, finding out that I just tried to scare myself.

Monero transaction is weird. It is like you buy a $5 goods, and you have $12. The weird thing is that you have to give all your $12 out in order to pay for the $5 thing , and then get $7 back, even though, you have $ 5 change.

What is wrong with it? So stupid, me and Monero. LoL.