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?
why should this be the first rule?
if you follow this rule you will certainly soon or late be a loser.
The first rule is:
buy if it goes up and sell if it goes down.
The usual beginner's error is to follow your wrong rule.
A beginner do buy when he starts...and sell when it is higher.
if it goes down...he waits and waits...
The old fox (lol) when he bought...and he sees that it goes down he is not afraid to sell (with lost) and so he can rebuy when it is lower.