for the life of

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.
See also: for, life, of
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

for the life of (one)

Though trying hard: For the life of me I couldn't remember his name.
See also: for, life, of
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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References in periodicals archive ?
"The amount of premium you pay goes into the policy design, especially on a traditional policy because you know you have a fixed premium often for the life of the contract.
For the life of every disciple casts a shadow across the lives of countless others, and each of our lives will either be an encouragement, inspiration, or guide for those who come after us.