It's the chrysalis. The pupa.
18 still remembers endless summers where fun is interrupted only by sleep. 18 can still feel the slip-and-slide on its belly, the cook-outs and late night games of Hide-n-Seek. 18 remembers snuggling on the couch when it was sick, having soup delivered in front of the TV. 18 remembers laughing so hard it farted.
18 sees these things in the rearview.
To see the road ahead, 18 has to look away. 18 will see the potential that lies in winding roads and steep mountains. 18 will know there are views at the tops it has never seen. 18 will feel the thrill of riding to the bottoms and the labor of climbing back up. 18 can't see the butterfly that lies ahead until it lets go of the rearview.
Knowing that, every once in a while, it can look back. Because it was fun.