What many people call having "done a lot of work" often translates as having gained many mental insights, read a lot of books, attended large group seminars, or shared deeply with like-gender friends. All these experiences are valuable, but they usually don't incorporate much of an emotionally experiential component. And none of this "work" puts you face-to-face, under emotional guidance, with your most intimate partner at the time when the most difficult issues between you are up.
Over the years we have talked with many women who said they felt much more emotionally advanced than their partners, but when they are in an experiential situation where they actually have to express their feelings cleanly and clearly, we find they are not as on top of it as they thought they were. We have also heard from many men who believe they, themselves, have covered most of the therapeutic spectrum. But, these men, when it really comes down to it, may have very little capacity to be with their emotional selves, especially when they are under the pressure of a difficult situation with their most intimate partner. Over the years we have discovered that only rare souls have much skill in consistently receiving feelings in their intimate relationships - a skill that is absolutely fundamental for those who have a desire to sustain passion in their relationships. This is not to say that emotional work is all that needs to be done. But our point is that people who operate primarily out of their intellectual aspects don't realize that their "thinking" often holds a much larger defensive component than they are aware of.
On occasion, one partner from a couple comes alone to a group of ours. That's fine-once. However our experience has been that participating in more than one group alone, without the partner present, can lead to problems. A lot is gained in a group; much is learned that would be much more difficult to take in any other way. But these are the kinds of lessons that are difficult to teach to a partner without some third-party assistance. Considering the tools and awarenesses and understanding and new language we give people in our groups, what works best is for both partners to be learning together at the same time.