I guess that depends on how you define "understand." There are many things I understand that I would have a hard time explaining to someone else, much less defining them. Most people who have spent enough time to master something would agree there are certain (possibly asthetic) aspects that they recognize but couldn't define.

Even when you get formal, there are limitations to how expressive any language can be.

https://en.m.wikipedia.org/wiki/G%C3%B6del%27s_incompletenes...

https://en.m.wikipedia.org/wiki/Tarski%27s_undefinability_th...