The abject failure of British Prime Minister Theresa May to get the United Kingdom’s (UK) Withdrawal Agreement from the European Union (EU) through Parliament on 15 January 2019, with MPs overwhelmingly rejecting it by 432 votes to 202, has been put down to a variety of reasons. Primary among them has been the question of the post-Brexit status of the land border between the Republic of Ireland and the UK’s province of Northern Ireland. Although an issue which was initially seen as of minor importance, the significance of the Irish border steadily grew over time until it became the main stumbling block in UKEU Brexit negotiations brought about by the decision of the British people to leave the EU in a referendum held on 23 June 2016. Indeed, the key term of the ensuing debate, namely ‘the Irish backstop’, produced such confusion among politicians, political pundits and the general public that the House of Commons, split between so-called Brexiteers and Remainers, decided to reject May’s deal out of hand. This article seeks to argue that, from June 2016 (the time of the referendum) up to January 2019 (the time of the first vote on May’s Brexit deal in Parliament), the issue of the Irish backstop was seriously underestimated before suddenly taking centre stage and ultimately sabotaging the Withdrawal Agreement from within.