different reasons. it could be because the relationship didn't have a strong foundation to beging with. then, sometimes couples allow the relationship to become stagnant and/or begin to take each other for granted. then, they allow themselves to become overwhelmed by the day to day grind and, therefore, no longer make time for communicating with each other. i think that is the situation that most couples find themselves in. odd thing about it is that the one will tell his/herself that is something were to be wrong the other will tell him/her about it so they do not need to inquire about anything, aka communicate, while the other may in fact have something going on but does not say anything about it, aka communicate, because he/she does not want to cause any worry over it. odd. communications is key, and relationships take work. honestly, i think we just get comfortable and inturn become lazy.