You can make a paper airplane without knowing anything about fluid dynamics. It could be crappy. You try making different variants and finally arrive at a good design, and even come up with a folding formula for the best airplane. All without having to understand how fluid dynamics works.

"No one understands quantum mechanics" is a bit of a meme. Scientists have a good grasp on principles, the math there actually provides some of the most precise predictions we've ever seen. What's not known is "why" and "what does this mean". The "shut up and calculate" motto works really well for coming up with solutions for practical applications. The philosophy of it is lagging behind though. And many in the field only care about this while having beers at the bar on Tuesdays.