expression
one blunder ruins all one's hard work
Proverb meaning that a single careless mistake can undo the results of long, patient effort. Literally 'one fart in a hundred days of sermons'.
百日の説法屁一つで、長年の信頼を一瞬で失ってしまった。
Just like 'one fart in a hundred days of sermons,' I lost years of trust in an instant with a single blunder.
A traditional Japanese proverb. The exact origin is uncertain, but it uses the vivid contrast between long, serious effort (one hundred days of sermons) and a trivial, vulgar mistake (one fart) to illustrate how easily hard work can be undone.