When you can do the proof, you actually do understand; you just may not understand your understanding (viz. the SMBC comic on Polish Hand Math; I think this is

When you can do the proof, you actually do understand; you just may not understand your understanding (viz. the SMBC comic on Polish Hand Math; I think this is it: http://www.smbc-comics.com/index.php?db=comics&id=1917 http://www.smbc-comics.com/index.php?db=comics&id=1917)