Happy couples tend to rate their partners higher in three key traits: conscientiousness, low neuroticism, and moderate adventurousness. Conscientious partners are intelligent, attentive, and motivated, which leads to increased love and admiration over time. Partners low in neuroticism are emotionally stable, owning their emotions and demonstrating life satisfaction. A moderate level of adventurousness is preferred over high adventurousness as it provides stability at home and a focus on simple things like family, which are crucial for long-term happiness.