"Design is nothing, content is what matters..."

If this were true, we wouldn't need to be constantly reminding people to not judge a book by its cover. That said, great novels have been judged so by their content, not their cover. So it seems that the whole of it is more complicated than any part.

Maybe something like: It must look good to get attention. It must be good to keep it. But if something that looks better comes along, it will steal attention, at which point you can only recover it if you remain better.

But that doesn't make a snazzy saying.