There is a reason for everything. Everything happens for a reason. Everything happens according to plan, no exceptions to The Rule.
A purpose, a reason, a time for every little thing, according to The Book, according to The Plan, according to The Rule.
Deviations happen, though, as a result of man's exercise of his free will which The Author Himself wrote up. Deviations occur when man, because of his sinful nature, chooses NOT to follow The Plan, NOT to stick with The Rule, NOT to go by The Book.