Belief can be either emotional, based on feelings, conjecture, blind following etc or it can be intellectual, based on rational thought, evidence.
Reality exists, but your perception is subject to doubt, but the existence of reality is not subject to doubt. God either exists or does not exist...that is a rational fact (in fact for those who engage in rational thought the existence of God is a rational fact)... There is a knock at your door...you can't see who or what is making the knock... It is a rational fact that something is making the knock, unless it is your mistaken perception, mishearing...but even that will have a cause also, as causality is a rational fact. People have their beliefs and perceptions but external to all of that is the truth, objective reality... So the discovery of that will not just be based on perception but rational thought, as rational thought can eliminate or affirm what is beyond the limits of perception, outside of it's scope and free from it's delusions and errors.
Your denial of the reality does not stop it existing and your ignorance of the reality does not stop it existing and your perception or knowledge of it's existence is not the cause of it's existence. One person believes God exists and another person denies that God exists, they can't both be right, due to the principle of non-contradiction... Two things which nullify the reality of one another can not coexist in the same instant. You are either alive or dead, you can not be both, unless you are talking metaphorically or referring to different attributes or using different definitions or meanings.
If people were to use rational thought to establish their beliefs they would not arrive at such false beliefs or doubtful ones. It is amazing that people use rational thought in their daily lives for trivial matters but they abandon it for the most important matters and are happy with following social-media slogans, conjecture, emotions, fashion, populist idiocy, uninformed commentators, false authority and imagination.
My video on clarity might help a little:-