Equal treatment is a myth.
Of course fair treatment goes without saying, but equal is silly. People have different skills, talents, different opinions, motivations and track records.
If you're a manager and two of your employees are underperforming, don't hesitate to treat them differently. If you know one responds better to the stick, and the other to the carrot...feel free to reprimand one and encourage the other.
You have to remember that your primary job as a leader is to get your people to achieve the mission, to get them to the promise land, to help them do work that matters.
If you're a manager and you're treating all your employees equally you're probably being unfair.