Below is a quote from Václav Havel on the importance of self evaluation for those in possession of power.
Being in power makes me permanently suspicious of myself. What is more, I suddenly have a greater understanding of those who are starting to lose their battle with the temptations of power. In attempting to persuade themselves that they are still merely serving their [organization], they increasingly persuade themselves of nothing more than their own excellence, and begin to take their privileges for granted.
Honest, regular self evaluation is extremely important.