But it wasn't obvious before the vote. At least not to
  the average voter.

I've heard it suggested [1] that the leave vote is indicative of a lack of trust in our political institutions. I think that's an interesting point of view, because it explains a lot about the recriminations about the result.

If you think our institutions are basically sound, and you hear dire warnings about brexit from government economists, national and foreign politicians, journalists, think tanks, business leaders, academics and industry bodies you'll naturally think "these well-credentialed experts all agree, only an idiot would ignore all these warnings"

If you think our institutions are unsound, and you hear dire warnings from the bodies that failed to predict or prevent the 2008 financial crisis and that told us Iraq had WMDs they could launch within 45 minutes, you'll naturally think "these bodies are just mouthpieces for the PM, only an idiot would believe all these warnings"

In other words, it _was_ obvious to _remain_ voters that we should remain - it just wasn't obvious to _leave_ voters because they approach the question with different world views.

[1] https://theintercept.com/2016/06/25/brexit-is-only-the-lates...