you don't understand
De repente, me parece que no entiendes el latín.
Suddenly, it seems to me that you don't understand Latin.
— 28 años después: El templo de los huesos (2026)
Aunque entiendas francés, no entiendes español.
Even if you understand French, you don't understand Spanish.
That's what you don't understand.
No entiendes lo que digo, ¿verdad?
You don't understand what I'm saying, do you?
— La vida es bella (1997)
You really don't understand, do you?
Tom entiende lo que no entiendes.
Tom understands what you don’t understand.
If you don't understand, ask.