Jealousy is a disease, love is a healthy condition. The immature mind often mistakes one for the other, or assumes that the greater the love, the greater the jealousy - in fact, they are almost incompatible; one emotion hardly leaves room for the other.

Heinlein sharply separates jealousy from love, treating jealousy not as proof of devotion but as a pathological response rooted in insecurity and possessiveness. By calling love a “healthy condition,” he frames mature affection as expansive—concerned with the beloved’s well-being rather than control over them. The “immature mind” he mentions reflects a common cultural assumption that jealousy measures intensity of feeling; Heinlein rejects this, arguing that jealousy crowds out the trust, generosity, and respect that sustain genuine intimacy. The final claim—near incompatibility—suggests that where jealousy dominates, what remains is less love than fear of loss and wounded ego.