you have no idea
You cannot imagine or understand. I'm sorry I'm late for dinner again. You've no idea how much stuff I have to get through at work right now. You have no idea what it's like raising two kids on your own while still holding down a full-time job, so stop criticizing me about my parenting!
you have no iˈdea...
(spoken) used to show that something is hard for somebody else to imagine: You’ve no idea how much traffic there was tonight.