How can some people not see that catholicism is a delusion?

The catholic church couldn't even calculate the days of Jesus' death right: he was dead for 3 days and 3 nights, yet they declared he died on Friday and resurrected on Sunday. There are so many made-up things in catholicism, like praying the rosary. When catholics see how it doesn't makes sense, how do they manage to cling on to it?