We are in a Brecit mess. Here's the first reason, from the Supreme Court decision today;
The 2016 referendum is of great political significance. However, its legal significance is determined by what Parliament included in the statute authorising it, and that statute simply provided for the referendum to be held without specifying the consequences.
The second is that the Leave campaign refused to issue a manifesto for Brexit. They deliberately did not say what Brexit meant and so no one knew what they voted for, and still don't. That division in the UK will now run for many, many years.
And third? No one found out how to leave the EU, starting with whether or not Article 50 was revocable.
As cock-ups go Brexit has been a mess from the start. And it will be to the end. And that's the fault of those driving the process.