Is it possible to become 'excellent' at both design and coding?

Please don't. Leave ad targeting algorithms to the unwashed people, Perl, etc. Let's keep functional languages pure from the scum of the earth that is advertisers.

Half kidding, of course.

Being a hybrid is difficult because of these kinds of situations. Even if you get to be very good at one or the other (or both), you're still perceived as inferior by virtue of your supposed "lack of focus."

Bullshit.

I had a hard time with this until I realized that I bring something rare to the table. The ability to traverse these two worlds is an immensely valuable trait. People like you are often the glue that binds great teams together, because you know both professions from the inside, and you're able to communicate with each in their own terms. You can add value constructively ("Here's a possibility that either side isn't aware of because they don't know what the other half can do") and prophylactically ("That's a bad approach to the problem, because the other team will get stuck hard if you do it that way"). You are uniquely able to hash out ideas to the show-somebody phase quickly, because you know how to supply all the requisite ingredients.

At the end of the day, hybrids like you (and me, and lots of others out there) have a harder time demonstrating value because it's assumed we are simply shallow generalists. I'm sorry to say that the onus will always be on you to prove them wrong, and you have to market these rare aspects of yourself. The effects of your presence in a company are often diffuse and hard to measure, which makes your task doubly hard. Welcome to the club.

There are many companies which are desperate for talent like yours. If you are like me, you'll feel unfulfilled working exclusively on one side or the other. Don't settle for a job that only draws upon half your talents—you are more than the sum of your parts. Keep growing both sides of you, and make "marketing myself" a learning goal for this year. :)

Well, some of these interviewers are recruiters, and they have to put me in a well-defined box in order to match me to a position. I have some sympathy there. But the others... are more disappointing.

But: I've found that the people and companies that "get it", really get it, and will reward you for it. Instead of asking about the "design" and "code" boxes, we can have actually useful conversations about subsets of skills within them (user experience research! graphics! Javascript! Python! databases!) What with my technical inferiority complex and such, such people value me even more than I value myself.

And for those that don't, well, when you create your own company down the road, it will build things that are neither vaporware mockups nor asstastic apps, and have a culture of "getting it" from the start, so you can eat their lunch. :)

If you're thinking about this inside of an organization, you have to decide what kind of person you want to be: the nail or the glue.

It's possible to not specialize and to be super valuable. You can even lead teams with this approach - as long as you're very cognizant of where your people are better at one specialty than you (i.e. your designer gets to make the tough calls, not you). When you straddle the lines, you're able to translate between experts and to make sure all of the little details are covered. Often, you are the reason that things stay together instead of splintering apart: the glue.

But if you really want to be able to call the shots and be the expert in an area, to lead the team and to be ultimately responsible for "X" - you need to be focused on it. You need to have the most clear understanding of the problems you're dealing with and the person who spends the most time working on and thinking about it. Your value comes from having a sharp and accurate point of view - the nail.

To those who say that you can be expert in both, the answer is that you're fooling yourself. The world that we live in is such that it's impossible to truly be an "expert" in anything. The best we can be is to be constantly learning through practice, education and discussion.

It's impossible to constantly be on top of code and expert in design at the same time because there's so much to learn about each area that splitting your time leaves you behind the truly focused individuals.

As an aside, while again i don't know if excellence in design and coding are achievable by the same person ,i suspect parity probably is. For instance, i'm an average coder and a bad designer, but with enough practice mediocrity in the latter should be attainable.