for the life of one
for the life of (one)
Despite one's best efforts; to any degree whatsoever. Often used in negative constructions. For the life of me, I can't remember where I left my keys! She couldn't understand for the life of her why people were so obsessed with celebrity gossip.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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]
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.