A mix of interest, a compulsion/obsession with learning the basics of anything to make optimal decisons, and get taken more seriously by experts (it turns out all it takes to get your optometrist to take you seriously is to use words like "autorefractor" and "phoroptor"), overconfidence ("I know RF, and light is an electromagnetic wave too, how different can it be?") and I guess also frustration (what do you mean, I need to renew the contact lens prescription every year, I can only be prescribed one type and I need your blessing to try 2-weeklies from the same brand, which you would have happily prescribed instead of the dailies? No thanks, I'll just import them then.)
But really, I've just worn glasses for a long time and nothing I wrote there is actually all that deep. I may have read a few papers.
