七年之病，求三年之艾
qī​nián​zhī​bìng​qiú​sān​nián​zhī'ài

to seek a late cure

七年之病，求三年之艾 qī​nián​zhī​bìng​qiú​sān​nián​zhī'ài
to seek a late cure
(proverb) to seek a long-term cure only after an illness has become chronic; used as a metaphor for waiting until the last minute to find a solution when it is already too late. From Mencius: if a seven-year illness requires mugwort aged for three years to heal, searching for the medicine only when the crisis arrives will be fruitless.