This is absolutely true. When I first attended therapy, one of my goals was to "improve my marriage". What I didn't realize then was how much I could improve by working on my own issues. You've allowed me to remember how much baggage I was bringing into my own marriage.
It was initially a goal of mine to get us to couples work together, but after working on my personal issues it seems much less critical than it did. By implementing several of these ideas, I've been able to gain many insights into my own behavior and subsequently improve our marriage.