for the life of one

for the life of (one)

Despite one's best efforts; to any degree. I can't for the life of me remember where I left my keys! For the life of her, she just didn't understand people's obsession with selfies.
See also: life, of

for the life of one

Although trying hard, as in I can't for the life of me remember his name. This expression is always used hyperbolically, that is, one's life is not at all endangered. [Late 1700s]
See also: life, of, one