Why Do People Believe?

Because people who don't believe in something usually don't live very long if at all.

It might be as simple as believing that you are going to grow up and meet someone and have kids.
That might be all someone needs to believe in.

It might be believing you will survive some awful time in your life or some calamity when everyone else around you is dying or injured.

It might just be believing that you will survive because all your relatives are dead.

Or it might be that you believe something really exotic or you might believe the religion that people around you are practicing.

In the end it might not matter what you believe in as long as you believe in something even if it is only believing in yourself to survive anything that comes.