To recap the puzzle:
1) A guy shuffles two boxes, one with twice as much money as the other, and we randomly pick one. Switching appears to be +EV because let's say that the box we picked has X dollars. Because 50% of the time we randomly picked the box with less money and 50% of the time we randomly picked the box with more money, half the time we'll get 2X and half the time we'll get 0.5X if we switch for an EV of 1.25X, which is greater than X. So for example, we see our box has $400, half the time switching would give us $800, half the time switching would give us $200 for an EV of $500. So it seems like we should always switch no matter what.
2) However, the paradox is that we can clearly see using common sense that switching every time doesn't actually help us since we could have just picked the other box to begin with.
So how can we resolve the paradox presented by 1) and 2)?