I don't think that's the assumption at all. Failure can - and does - happen to everyone, and doesn't on its own imply incompetence. We all make bad assumptions

I don't think that's the assumption at all. Failure can - and does - happen to everyone, and doesn't on its own imply incompetence. We all make bad assumptions and bad projections, and that's part of the game. But an incompetent executive will avoid making decisions altogether, and will pretend to lead by setting goals that are entirely detached from reality. In my experience, the lack of decision making and inappropriate goal setting is quite obvious to those of us "in the trenches". You can't, for example, expect to triple your sales in the next quarter unless you're doing something to support that goal, like increasing the size of the sales team or doing more marketing. But I have worked for people who have set sales targets thinking that this is all that's needed to make sales. These people are good at talking about the "what" but no good at working out the "how". There is strategic thinking, tactical thinking and wishful thinking. Incompetent executives generally operate using the latter framework.