A relationship is similar to the launch of a space vehicle. When NASA launches a space vehicle, it uses about 90% of its fuel getting beyond the earth’s atmosphere. After it clears the pull of this gravitational force, considerably less fuel is required, allowing it to travel great distances expending much less energy.
This principle also applies to relationships.
The secondary stage (after you pass the delirium of infatuation) is where the real work begins. That work is about committed listening, letting go of control, practicing vulnerability, overcoming resistance to change, being honest, even in the face of fear, and focusing on your own work rather than trying to change your partner. Like mastering any other new skill, it takes a lot to hang in there and muddle through the demanding times.