"why"...because I'll forget ;)

Why questions are the most difficult for Jackson to answer. He's gotten really good at "what", is decent at "where", we're working on "when"; but "how" and "why" are so abstract and difficult for him...
Last month he answered his first why question. The other day I couldn't even remember the answer, so I'm putting here forever...
We were at my grandparents hanging out with them, (my uncle had just passed away). Jackson loves their house. They have all the cool things he likes: lots of space to run, a long paved driveway to ride his bike or scooter, a barn full of tools, a swing, the list goes on. He'd been outside playing, riding his scooter and he came in and asked to go to the barn. It went something like this:

J: "barn?"
Me: "what do you want?"
J: " I want to go to the barn please"
Me: "Jackson why do you want to go to the barn" [of course I wasn't expecting an appropriate answer]
J: "to ride the tractor"
Me: [to my grandparents] "That's the first time he's ever answered a why question, I'm taking him to the barn"

So, we went to the barn so he could "ride the tractor".
My life is filled with simple joys so many others take for granted...