"He failed at/on life."

Should it be "at" or "on"?
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Comments  (Page 2) 
Let's try more-common-person examples:

"He failed at/on simple tasks."
"He struggled at/on simple tasks."
SheltieBites"He failed at/on simple tasks.""He struggled at/on simple tasks."
I believe the most natural prepositions in those sentences would be:

"He failed at simple tasks."
"He struggled with simple tasks."
Students: Are you brave enough to let our tutors analyse your pronunciation?