Riddle: How is a 2-year-old like a train?

"Choo-choo!" exclaimed Michael, as if were his first time seeing a real, live train. Actually, we see these same trains every week or two when we go to Grandma & Papa's house. I long for that ability to so live in the present that, like a small child, I can always enjoy my current experience as if it were my first time. But my story's gotten derailed.

"Choo-choo nigh-night," he observed. Indeed, the train was dark and sitting still on the tracks. He expanded on his point: "Dat choo-choo not going, choo-choo nigh-night. That choo-choo doe nigh-night dust wike me!"

I laughed. "Yes, the train does go to sleep, just like you." I hadn't seen if from that perspective...