It's about belief of capacity for change:

The good news for those who are skeptical of a partner's ability to change: with self-awareness and effort, you can convince yourself that your partner's effort does matter and that your relationship can improve.

"A secret to building a happy relationship is to embrace the idea that your partner can change, to give him or her credit for making these types of efforts and to resist blaming him or her for not trying hard enough all of the time," Molden said.

Thanks Adam.  I took note of that quote as well.  The only problem I have with the study is that they don't seem to acknowledge that it may be true that your partner is not really making an effort, and how to tell the difference.  I think that that is crucially important.

It's hard to tell the difference! That's why there is couples therapy -- to get a third party who can observe.

I see it very differently.  A therapist is in no position to observe either one of the partners' behavior day-to-day.  But research evidence seems to suggest there are specific behaviors that ANYONE can learn  to observe that makes a difference in how successful the couple be.  Perhaps that's why videotaping the couple for quite a couple of in the LOVELAB was such an effective way to predict marital success or failure.