Believing is not the same as considering something true. When you don't have enough empirical data about something, you can only believe that it's true, if you want to.
Once you have empirical data, you can begin to consider that thing true. That's where believing turns into knowledge.
No one here who hasn't seen someone's arm get severed knows what happens when someone's arm gets severed. When you ask person A, they're gonna say that the person bleeds to death. When you ask person B, he's gonna say the muscles tighten so that they won't bleed to death very fast. When you ask person C, he's gonna say that it depends.
You still do not know what happens when someone's arm gets cut off. You can only choose to believe what some people tell, based on their arguments, and what is most plausible. When you see it happen, or if it happens to you, you see how it happens, and can call it knowledge.
Let's assume person A was right. The guy who lost his arm bled to death in a matter of minutes. However, this does not rule out what person C said: "it depends". It could be that another individual's muscles tighten around the wound, or what the heck ever, and that individual does not bleed to death as fast. We do not know if person C was right, but it's still a possibility.