Yes, lying to the people is bad, and cheats them out of good things. But lying to yourself, and cheating yourself out of what you could have been, is far more cruel and far more permanent.
Literally: self – self – deceive – deceive
Alternately: Fooling or lying to oneself. By extension: to betray one’s true feelings (or worse, one’s conscience) with false words and deeds.
Notes: Be careful not to write 己 as 已 (i, “stop”) or 巳 (shi, “snake [from the Chinese zodiac]”)