Is it better to have someone earn your trust? Or to give someone the benefit of the doubt and trust until it is broken??

Hmmmm ? I see trust from both sides now, but I really don't know trust at all. ;) I kinda lifted that line ( not word for word obviously) from Joni Mitchells song book, but I think it applies here. Earning someone's trust is important, but then, we are all innocent until proven guilty, are we not?