An old
expression that denotes an inability to
keep perspective when one is striving for power. (Political, financial, personal, whatever).
The idea is that you become overwhelmed with the pursuit and
lose sight of those around you, usually resulting in loss of respect, friendship, family, etc. aka:
tunnel vision.
Also the name of the autobiography that John Dean wrote after the Watergate scandal in the Nixon White House.
Closely related to another old expression:
Power corrupts, and absolute power corrupts absolutely.