At first I wondered how I was going to answer this question, because it really jumped out at me. How to stay hungry?
For me it's real simple. Hack the hunger back in.
If I stay in the same geographic place, do the same job, go through the same routine, I lose my hunger entirely.
So every few years I try to reset my life.
Move to a different place. Changing jobs. Changing companies. Change my circle of friends. Travel to a place where I don't speak the language. Take on a new challenge. Do some fasting.
In other words... rip yourself out of your comfort zone.
Your hunger instinct will come right back again. Because you're wired to bring yourself back to a comfortable position once more.
Think of it like this -- you set off on a long journey where something desirable awaits you. Are you going to give up? Likely, no.
Set yourself on new journeys every day. Large and small. Hack the hunger.