there's method in madness

there's method in somebody's madness  (British, American & Australian) also there's a method to somebody's madness (American)

something that you say which means that although someone seems to be behaving strangely, there is a reason for their behaviour

Usage notes: This phrase comes from Shakespeare's play 'Hamlet'.

When he picked the side I thought he must be crazy but, judging by their performance this season, there's obviously method in his madness.

See also: madness, method