If all people, including yourself, become corrupt when given power, then why shouldn’t you seize power for yourself? On average, you’d be no worse than anyone else, and probably at least somewhat better; there should be some correlation between knowing that power corrupts and not being corrupted.
Knowing power corrupts, a self-interested individual would seek to surround himself with those who did not seek power (or at least did not seek power that could be wielded against him). These individuals would not be likely to put up with people who sought power with the potential to do serious harm, so it would be advantageous for this self-interested individual not to seek power at all (or to do it clandestinely).
Grant comments on Why Does Power Corrupt?