Doon's father is "a tall man, bald as a peeled potato, with a high forehead and a long chin. He had kind, slightly puzzled gray eyes" (3.42). He's Doon's biggest cheerleader, constantly encouraging his son to learn more about the world in order to change it for the better.
So when Doon comes home from his first day working in the Pipeworks, his father listens to him complain about the generator situation, then says: "You'll think of something. You're a clever boy. The main thing is to pay attention. Pay close attention to everything, notice what no one else notices. Then you'll know what no one else knows, and that's always useful" (3.50).
This attitude makes sense when we consider that Doon's father works at the Small Items Shop, "which sold things like nails, pins, tacks, clips, springs, jar lids, doorknobs, bits of wire, shards of glass, chunks of wood, and other small things that might be useful in some way" (3.38). Given this profession, we can see why Doon's father is used to paying attention to the little things in life, and finding some use for them. Then again, this must be a pretty common trait among Ember citizens, given how much they need to recycle and reuse their daily items.
Of course, Doon doesn't always get along with his dad. For one thing, their temperaments are pretty different. Doon's a bit of a hothead while his "Father doesn't even have a temper […]. He's as mild as a glass of water" (6.41). Mildness isn't always an asset in Ember, where you've got to fight for your own safety, but his peaceful demeanor does keep Doon cool in his hotter moments, so there are some benefits to his dad's cool, calm, and collected demeanor.