My glasses are optical, so I suppose they are used more intensely. I have to take a better care of them as I highly depend on them - cannot part with them to send them to nowhere and cannot treat them with hazard hoping that they will survive anyway and then say: look a miracle. Yet if an emergency arose I can get them fixed at the spot. In the end I am fully aware that vast majority of US customers in the area of metal optical frames wear titanium and are happy with them. After the stunning lesson I had, though, it would have been highly irresponsible of me (less PC adjectives could be put here) to put such a failure point in my system for no perceivable gain, in fact loss. A minor incident in my case turned into a major disaster - fortunately my trip at the time was winding down so most loss was financial - I had to get new glasses at 2x I would have paid at home + alter personal plans to get the glasses done + weigh on the neck of my hosts to help me.
Not having a spare pair of glasses with you at all times when you are dependent on them is not what i would do.
When most people can get a second pair of glasses for $100-200 traveling without a spare seems silly to me.
yup you might not be as hansom in your backup glasses but---
There is an old saying---two is one, one is none...
I try to have duplicates (or triplicates) of nearly everything in my life----please don't tell my girlfriend (s)