You have to convince them that you know what you're talking about. If it's too vague, it suggests that you don't know what you're talking about, or that you don't enough about your goals to talk about it in a credible way.
From what you wrote, it boils down to "I want a really important job where I can make big decisions for a business" which won't hold water because it suggests that you haven't really dug deep enough to figure out what that really means. Because the more you research and get informed, the more specific you will be.
It's not about lying or choosing something specific out of thin air -- it's about actually doing more legwork on what it is you want.
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