Buy low and sell high is the first rule of trading.

But you can buy high and sell higher, or sell low and buy lower also.

By selling highest you get the advantage of selling with a profit even when you have bought also high. By buying real low, you get the profit of not having to sell at a certain margin. You can wait till profit goes really really high.

Lets say a genie gave you the ability either to sell at the daily maximum or to buy at the daily minimum. What will you choose?