kathy ,,,,,it always works because two people works on any relationship to make their life perfect .an individual person is not perfect and he/she always have some kind of emptyness in life which he/she try to fulfill by means of other person.if both are same then they have common problems and who can solve their problems...which lead to breakup.for example consider me i m very short tempered and if my partner is also same like me then we get fight every second because no one understands each other problem so no one compromise .