I remember a client at a previous job claiming an app we were developing for them was definitely going to get "millions of users" in only three weeks after release, even with a small marketing budget. I laughed at how crazy unrealistic that was.

I bet they would look at these numbers and scoff, even though it's still an excellent number and I know they didn't even breach 50k users several months after release (I was no longer on the project after that point).