Stagnation is an deficit of adaptation to the world around us, and adaptation is a major gift of the virtue of Philosophy. And so Stagnation is the deficit of Philosophy. A person who is "a lump on the couch" or on the more positive, "in a rut" in terms of how they approach goals. It's hard to get them to pursue their own goals, let alone concoct JOINT life's goals.
Philosophy as a virtue, is composed of curiosity and maturity, and so the excess of it turns us toward a kind of voracious curiosity that actually is detrimental and immature to ever getting to our goals. Whereas the virtue of Philosophy in its curiosity contributes to us being adaptable to the changes in our environment by seeing challenges coming our way and seeing the possible strategies to solve them, the maturity in our philosophy also causes us to be adaptable by actually having the psychological balance and resources to solve those challenges. As a result, Stagnation is harmful to the individual, and to the relationship, in its pathological narcissism and immaturity.