don't push yourself too hard; don't force yourself
A colloquial fixed expression used to caution someone against overexertion or unreasonable effort.
You're still recovering from your illness, so don't push yourself too hard.
If you're tired from pulling all-nighters, you shouldn't force yourself.
A set phrase combining 無理 (unreasonableness, overdoing) with 禁物 (something forbidden or to be avoided). The exact origin is uncertain, but it follows the common pattern ～は禁物 used to warn against a particular action or state.