Beliefs come from 'believing', that is, accepting what is told to us by figures who weald authority and credibility in our lives. However, our own experiences sometimes prove these to be erroneous, sometimes even completely false at times - hence many an argument with parents, relatives and even teachers as time goes by.
There is a problem that once we accept a belief, whether it be induced in us by others or by ourselves, we tend to strengthen it by our bias. For example, the publications we read, and the people we deliberately choose to mix with.
Really, the only things we can be absolutely sure of are those we have experienced first hand. But these are no longer beliefs but KNOWINGS. If we're true to our knowings, then we can't go too far wrong in our lives. But even here, we need to keep an open mind for even the things we know are subject to change.