Fighting for the user.
Bob Messerschmidt's company was acquired by Apple and Messerschmidt ended up working on the heart rate sensor for the Apple Watch. That involved interacting with Jony Ive and the Industrial Design team, and learning how Apple builds products.
One great example is [when] I went to a meeting and said I'm going to put sensors in the watch but I'm going to put them down here (he points to the underside of the Apple Watch band he's wearing) because I can get a more accurate reading on the bottom of the wrist than I can get on the top of the wrist. They (the Industrial Design group) said very quickly that "that's not the design trend; that's not the fashion trend. We want to have interchangeable bands so we don't want to have any sensors in the band."
Then at the next meeting I would go "we can do it here (on top of the wrist) but it's going to have to be kind of a tight band because we want really good contact between the sensors and the skin." The answer from the design studio would be "No, that's not how people wear watches; they wear them like really floppy on their wrist." That creates a set of requirements that drives you toward new engineering solutions.
That's kind of what we had to do. We had to listen to them. They are the voice of the user. There's the whole field of Industrial Design that focuses on the use case, the user experience.
Apple thinks about feature sets, not chipsets. That's a subtle but fundamental difference when it comes to their products. If you take a piece of technology and try to figure out what to do with it, the product always feels like an afterthought. If you take the product and figure out what technology you need to realize it, then the product feels realized.
(Arguably, Apple Watch struggled with that in the first generation.) In a perfect world, every product, Apple and otherwise, would have an executive ruthlessly cutting for its realization.
Messerschmidt also shares some thoughts on aspects he didn't like as much — including secrecy. Well worth a read.