Yesod is both the “foundation” on which our other traits are built, and bonding: it bonds together the sefirot above it.
The connection is perhaps reflected in the expression that someone has “his act together.” Having your act together is a good foundation, a good basis for a healthy personality.
Psychologists talk about the “integrated personality” as a healthy personality. Things are balanced. In our kabbalistic scheme, there are appropriate amounts of the traits above, love, discipline, etc., in balance.
The balance goes beyond just our personalities – we also need to balance different realms of our lives, body, mind, and soul. It’s a good practice to find time everyday for things that nourish all three — exercise, thinking, and prayer.