According to Walter Isaacson – the bestselling author of their biographies – it is this:

I started with Ben Franklin, and then Einstein, and then Steve Jobs—[they were all] innovative and creative. And I said, “Well, what pattern [leads to] that?” The pattern wasn’t that they were smart, because you’ve met lots of smart people, and they don’t usually amount to much. The pattern tends to be curiosity across disciplines.

This excerpt was taken from a conversation between Isaacson and Adam Grant, which you can read or watch here. 

Here is another excerpt that speaks to the way in which Jobs prided himself on working at the intersection of technology and the humanities:

I’ll give you a tiny example. The Mac that came out in 2000 had a handle on it, and they say, “This is a desktop machine. We don’t need the handle—people aren’t really supposed to move it around. It’ll cost us another sixty dollars [per computer].” And Steve said, “The handle is there because it makes the machine approachable. My mom is afraid of her computer, but if there’s a little thing [where] she can put her hand, where she can touch it and she knows it won’t break, that makes her connect emotionally to the computer better.” And he was right. But it cost money, and the Mac didn’t make as much.

The entire conversation resonated with me partly because I think of development as being a career that, by necessity, requires you to work across disciplines. 

I also sometimes wonder if I have too many broad-ranging interests. It can be overwhelming. But apparently that’s a good thing for innovation and creativity.