Georg Petschnigg, co-Founder and CEO of FiftyThree, in an interview at 99u:

There’s a simple question we ask when we’re thinking about bringing a new person onto our team: are they good at a minimum of two things? And that could be something like software development plus playing the trombone, or visual design plus film making. This is important because it’s really humbling to become good in yet another discipline, if you’re just good at one thing it’s easy to believe that you actually understand it and are the expert. But when you try to learn something new, like another language, you’re instantly humbled. And that’s really important to us, because we believe that creation really happens when boundaries are crossed.

Being good at two things doesn’t mean that you’re “master of none”. It’s the exact opposite—being good at several things make you better at all of them. Every single day, I work with programming and design. When I wake in the morning, the first thing I do is study French. Rather than turning to audiojungle, I decided to produce all the sounds on my own for my upcoming iOS game SpellRush.

I started broadening my focus about a year ago (at that time I worked at Spotify as a Product Designer), and although I’m now splitting my focus between more things, I’m learning more about design now than ever. And juggling several disciplines not only keeps you humble and hungry to always learn more, but it also makes it easier to look at things more objectively.

If you’re only working with one discipline, you’ll most likely look at any problem through that discipline. If you’re a programmer, it’s easy to blame a product failure on bad programming. If you’re a designer, it’s easy to blame a product failure on bad design. When you have experience with both, you learn to see how everything comes together, see the big picture, and pinpoint the real problem.

The extended version of the “Jack of all trades” expression is more appropriate:

Jack of all trades, master of none, Certainly better than a master of one