The two ideas of knowledge and attitude aren't mutually exclusive. And one isn't necessarily more important than the other. The context matters. But in the context of starting and running a successful business you need more than just skill or a good idea.

I find understanding people and effectively communicating essential skills in business. Also I think starting a business is different from running a successful established business, which is further different from running a large corporate entity. But in all of them you have to have a vision for where the company should go. Your idea should be something people need/want/don't realize they want. You have to be able to outline what's important and be able to get that out of others. You can't do it all yourself.

Though I don't think I'd call those interpersonal relationship skills "attitude".