Why do so many believe that if something isn't in the bible, it must be wrong?

Well, after the split from the Catholic Church, most protestants stated that the Catholic Church is wrong. To accomplish this they had to attack most things the Catholic Church did that wasn't in the Bible (even though all Jesus commandment weren't written in the bible, but passed on through the first christians and thus created the Catholic Tradition). The decided sola scriptura, and thus moved farther from the original churches (Catholic and Orthodox)