Is there an idiom or slang for "When you put all of your efforts on something but it doesn't even meet the minimums"?
Solution 1:
A common idiom for futile effort is: "Trying to hold back the tide with a broom." (US) (Sorry, I don't have the resources to find its origin - but there's probably someone on this site who can edit this properly.)
Two references: John Bartlett, Familiar Quotations
AUTHOR: Sydney Smith (1771–1845) QUOTATION: In the midst of this sublime and terrible storm [at Sidmouth], Dame Partington, who lived upon the beach, was seen at the door of her house with mop and pattens, trundling her mop, squeezing out the sea-water, and vigorously pushing away the Atlantic Ocean. The Atlantic was roused; Mrs. Partington’s spirit was up. But I need not tell you that the contest was unequal; the Atlantic Ocean beat Mrs. Partington
Elizabeth Robbins: Staging a Life
During the reform agitation of 1830-2, the figure of Mrs. Partington had been created, trying in vain to hold back the tide of change with her broom.
Solution 2:
[...] best wasn't good enough
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The song Just Once by James Ingram has this opening line (See You Tube) ...
I did my best, but I guess my best wasn't good enough
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Another similar song usage in Anouk's track title:
My Best Wasn't Good Enough
Solution 3:
Your efforts
Fall short (dictionary.com)
Prove inadequate or insufficient. For example, His skills fell short of the required standard.