Well, I'm not arguing that Cameron was a twit (typo), but still -- it wasn't simple. Firstly, we had to leave in compliance with both Article 50 and according to our own constitution, and secondly we had to have at least some idea of what we wanted to do with leaving -- that whole "soft v. hard" Brexit debate of 2017/18. Now the debate has been over what sort of compromise deal to reach, and really it's all about the Customs Union. Oh, and the Irish border issue, which has proved to be impossible to solve to everyone's satisfaction -- ie, everyone agrees that the necessary consequence of leaving the Customs Union is to introduce some kind of border somewhere in or around Ireland, but where? Along the actual border violates the terms of the Belfast Agreement, and along the Irish Sea is understandably offensive to Unionists.