For David and me, thankfulness is a kind of Superglue. It's more that we've become deeply convinced that God will keep on working in us and through us, no matter what comes our way. In that sense, a thankful spirit is giving our marriage a sense of glad expectation. Thankfulness defeats gloominess or feelings of hopelessness about our marriage. When we're thankful together, we're helping each other put our faith in God.
Thankfulness is binding because it requires some humility.
You can't be thankful and boastful at the same time. David is humble enough to know whom to thank for his talents, his health, his family, his job. The humble aspects of thankfulness remove the necessity of power struggles between us. So I'm thanking God for my thankful spouse. As different as David and I are, we need this foundational point of connection.