When we say that someone "sticks to" a certain task, idea, or opinion, it implies that they are committed to it and won't waver easily. There are many other words that can convey this sense of determination and steadfastness, including "adheres to," "clings to," "holds fast to," and "perseveres with." Other synonyms that may be appropriate depending on the context include "follows through with," "doggedly pursues," "maintains," and "sticks by." Whatever word or phrase we use, it's clear that someone who "sticks to" something is someone who is reliable and unwavering, able to see things through to completion.