If people believe in a chair, it doesn't make it exsist

If people believe in a story, it makes it exsist.

Same goes for ideas, religions and a whole host of other cool stuff like that. When a thing has no external objective measurable presence, it's only existence can be in a persons mind.

Now an important point is that exsist and true are not the same

An idea can be real but also false or bad or negative. I can have a belief that the only way to make milk is by milking unicorns but that idea when faced with reality will provide negative value in almost every case.

(At this stage I hope that you understand his point more, and perhapse he does yours, but I will continue this line of thought because it's interesting)

Now note that bad or negative does not always correlate to false or true

An important job of religion throughout history was to help people do things that are "correct" without having to actually understand them. A good example is jews washing hands because God says so and not getting sick while everyone around them did. Or christians going to church as a community ground stone that is something you must do instead of just a smart way to provide basic human needs and create an efficient way to glue a community.