Simple actually I sell when the price is high and I buy when the price is cheap
And today it's up to you if you want to sell, I find the price now as high because I started bitcoining when the price was less than $600. But it's also better to keep on holding.
So I get the profit from the difference between the sale and purchase
It's trading this is on how we are getting profit, the difference from the buy and sell rate. Of course we will sell if the selling rate is higher than we bought it.
Thats pretty obvious. Only a dump will sell off bitcoins at price higher than that at which he bought coins. Everyone wants to make profit with bitcoins and the easiest way is to take them out of wallet when prices are quite high. I personally prefer to hold onto bitcoins when they are dumping and cash them out when prices are on way to moon.