How can one explain it when otherwise rational people take irrational actions?

(For instance, giving all their hard-earned income or their family land to a fellow human as "firstfruit offering "; habitually punctuating almost every sentence with "My pastor said" or "According to Dawkins/Hitchens..." )

The fact still remains: no matter how weird the actions may look to you, they still made sense to the person involved.

Could it be because of a lack of understanding?

If you don't personally connect the dots yourself, you risk being a zombie to any nice-sounding idea

All ideas have logical conclusions which we are to find out for ourselves before we apply them to our lives.

Thank you