A bozo is someone who thinks they are much smarter and capable than they actually are. They constantly over-estimate their abilities and under-estimate the risks and threats around them. They typically don’t keep an open-mind. They look instead for data that confirms a previously held bias.
The article includes great quotes from Steve Jobs over the years and points to, in at least one small way, why Apple has been able to stay focused and "bozo-free" for so long.