Intimate relationships are psychic excavators: they help us heal by uncovering emotional relics we have inherited from past relationships. These relics are typically things that hurt--a lot.
We humans are skilled at protecting ourselves from pain by keeping it as far away as possible.
This is why partners blame, lash out, avoid, withdraw, or act out in other ways (e.g., lie, cheat, etc.).
Even though one or the other partner's behavior may be the most conspicuous source of relationship stress, the overall health of the relationship improves faster when each partner is willing to take responsibility for his or her own contributions to the marriage.
As a couples therapist and counselor, I often hear many different versions of, "If my partner/friend/family member would do more of this or less of that, I would be SO MUCH happier." Seems many of us believe the road to contentment is paved with another's intentions.
When a loved one's behavior is overtly destructive, would a change likely do everyone some good? Sure. However, when we focus exclusively on someone else's motivations or actions, we forfeit our own power to affect change. A pointed finger merely identifies the person to whom we have relinquished it.