The Bregret from those who voted to leave seems to be either 1) I wasn't clear on what I was voting for, and 2) I dislike the EU and voted to leave as a protest, but didn't truly believe many others would do the same. And then there are the people who genuinely wanted to leave the EU, but now regret that vote once they see what is happening to their economy.
There are many things in life for which you can have a mulligan (to borrow a golfing term - a do-over) or at least, a way out. Whether it's buying the wrong thing, accepting the wrong job, or even getting in a relationship with the wrong person, there are ways out.
The same is not true with voting. Once you cast your ballot, that's how it is. You don't get to change your mind later.
Let this be a lesson, America. In November, when you step up to vote, remember that you only get to do it once. You don't get to take it back after you see how everyone else votes, or after you see how awful the winner could be. Think through how you're going to vote. Listen to people when they discuss what could potentially happen if a certain person wins.
A vote is not a protest. A vote is not an experiment. You only get one shot. Don't throw it away.