Beware of anyone stating that they know something that they cannot possibly know. Believing something is very, very different than knowing something.
In science, there is a relatively strict methodology that ensures that the best approximation of truth is considered the prevailing notion. Some things can be proven to the point of being considered for all intents and purposes a fact. Some things are explained by tons and tons of evidence, but absolute certainty is unattainable. It's important to have in mind just what level of certainty is demonstrable in stating something is a fact.
Religion is, by contrast, mostly a matter of faith. Most religions make myriad byzantine claimes that are totally unprovable. Claims that cannot be tested scientifically. There is nothing inherently wrong with this, as you have to make certain assumptions in life, often without the benefit of rigorous scientific proof.
However, when it comes to the topic of what other people should believe, I think it's somewhat improper to expect them to believe things they don't currently believe without something approximating a compelling case. I've never really understood how someone can tell a story like, for example, the Biblical account of creation, and expect a single other person to believe it's literally true. It's so bereft of corroborating evidence, and indeed contradicted by mountains of physical and theoretical evidence that it strains credulity. It further strains credulity to think that a deity would make our eternal existence dependent on unsupportable and fantastical tales written by desert nomads 2000 years ago. That's not to say it isn't all true, it's just not supportable.
This goes for everything you hear, not just religious matters. Consider whether the speaker COULD know what they are talking about. Consider the supporting evidence. Maybe anecdotal tales of life-changing relationships are sufficient for you. Great. Just don't expect it to be enough for everyone else.
Capslock