“What does ‘If I didn’t know better’ mean?” —or even more casually— “What does it mean when someone says ‘If I didn’t know better’?” You could also say: “Can you explain what ‘If I didn’t know better’ means in this sentence?” “What’s the meaning of ‘If I didn’t know better’ in this context?” Phrase: If I didn’t know better, I’d swear you did this on purpose. Meaning: The speaker is saying that something looks or feels intentional, even though they know it probably wasn’t. So, it’s a polite or playful way of saying: “This really seems like you did it on purpose... but I know you didn’t. Or at least, I hope you didn’t!” Example: You brought my favorite snack and my favorite movie... If I didn’t know better, I’d say you were trying to make me happy! (= It seems too perfect to be a coincidence.)

It means to have common sense about something. Not taken for a fool or being dumbfounded.