The title says it all for the most part, but as a young entrepreneur whose skills lie particularly in design and marketing, should I invest the time in learning a language or two or stick to what I know and focus on doing them better? It seems to me like the more successful startups are coming from those who bring the company from idea to product completely from their own work.

I've heard arguments on both sides of the fence, and am curious what YC members have to say on the topic.