Alas, “deep” doesn’t rhyme.
(Nandemo koi ni meijin nashi;
“There are no masters of Whatever May Come”)
A person who is ready for anything, is not a master at anything. You can be a generalist or an expert, but not both. “A Jack of all trades is a master of none.”
We begin with the noun / question word 何 (often nani, here contracted to nan). This generally translates into English as “what,” but here we see it joining up with particle でも (demo), “but,” “even, “ etc. to form an expression meaning “whatever,” “anything.” Next comes the verb 来る (kuru), “to come,” in imperative form. The above act together as a single noun phrase indicating “[the kind of person who is] ready for anything.”
This noun phrase is marked by the particle に (ni), in a sort of attributive function, as the thing “to” which the following clause applies: the noun 名人 (meijin) – literally “name person,” figuratively “master,” “expert,” followed and modified by the adjective なし (nashi), “not,” in conclusive form.
A pithier synonym is 多芸は無芸 (tagei wa mugei), “many arts is no arts” or “versatility is equal to a lack of talent.”
It’s acceptable to write 何 in kana as なん, but for whatever reason none of the versions of this that I’ve seen write なし in kanji as 無し.
(“Kodomo no toki, eiga no eikyou kara ka, kagakusha nara soutairon kara kuroon no sakusei made nandemo kandemo wakatteru nda to omoikondeta nda. Dakara, daigakusei ni natte, nandemo koi ni meijin nashi to iu no ga genjitsu de, bunnya wo kimenakya datte iwareta toki wa, shokku datta nda. Sono shokku mo seichou ni fukaketsu na koto nan darou na.”)
[“Maybe it was because of what I saw in movies, but when I was a kid, I thought that scientists knew about absolutely everything, from relativity to cloning. So it was a shock when I got into college and they told me that in actuality there are no experts in Everything, so I’d need to choose a field. Maybe that sort of shock is an indispensable part of growing up.”]