Yes, it is possible to break an optical fiber by bending it too much. Mechanical Stress: One of the most common causes of bundle tail fiber failure is mechanical stress, which occurs when the fibers are subjected to excessive tension, bending, or twisting. This type of stress can cause the fibers to break or become damaged, leading to loss of signal or complete. As long as it's coiled using the right hand rule, it will provide negative feedback. Otherwise you'll get positive feedback, which will boost not only the noise, but your ego too. You jest but young me thought that connecting a second Cat5 run from switch to switch would increase bandwidth. Damage may not always be obvious, like a kink in the cable, but may include broken fibers, fibers with higher loss due to stress and cable structural damage that may lead to reliability problems.
[PDF Version]