A fusion splice or mechanical splice is only ever as good as its cleave. Improper cleaving, a dirty cleaver, or a dull cleaver blade can result in cracking or chipping in the fiber endface. It's also always important to clean BEFORE you cleave. Nothing should touch the end of your fiber once it is cleaned. After cleaving, the fiber should go directly into the fusion splicer fiber holder clamp or into the mechanical splice.