There have been numerous other surveys throughout the years including by Gallup [1] that generally all find similar results. The Gallup poll, though, was less precise and simply asked if people expected to become "rich." A directly related little datum that shows up in numerous polls is that approximately 90% of Americans think they have average or above intelligence. Average in this case of course is going to be interpreted as median.

I don't necessarily think it's arrogance so much as delusion. For instance a person paying tens of thousands of dollars for a degree of minimal utility obviously knows that this is a very bad decision deep down, but it's something they want to do - or perhaps they feel like they could not cut it in something like a STEM field. So the rationalizing kicks in. Maybe they'll become a lawyer, an author, or a speaker. They'll make millions! It'll be great! Of course it's just cognitive dissonance and self delusion.

[1] - https://news.gallup.com/poll/7981/Half-Young-People-Expect-S...