Are optical fiber fraglle?
Glass fibers are very brittle, actually in any glass light guide there is a percentage of fibers broken throughout the manufacturing process, conversely, since these light guides are sheathed, once installed are extremely resistant to external affects.
Bare PMMA fibers are extremely delicate throughout manipulation and manufacture, requiring great handling care. Once sheathed are almost impervious to external damage.
Another solid cores fiber is very tough due to an external Teflon cladding and can be installed without any type of problem. The only drawback with this kind of optics is the hardening with age that makes these conductors brittle and prone to shatter.