Just an FYI: you probably (almost certainly) do not know everything you think you know. (I know I do not, which, perhaps, makes learning new things daily much easier for me in a way.)
No one’s knowledge is exhaustive, even in areas of professional specialization. KNOWING that there is always more “out there, somewhere” to learn about every topic one is aware of (there are many topics that you and I aren’t even aware are areas of knowledge–think on that one, eh? 😉 ) can, if one lets it, encourage one to just keep on learning.
A day w/o learning something new–even, or perhaps especially, when it is something new about something “old,” old knowledge to us–IMO, is a day wasted.
Just sayin’.