One of the fundamental risks of a 'No Deal' Brexit would be the loss of a transition period between the United Kingdom's (UK) departure from the European Union (EU) and the entry into force of subsequent agreements establishing the future relationship between the UK and the EU. The idea of a transitional period of legal and economic continuity and certainty was suggested by the UK Government at the outset of the Article 50 TEU negotiations and accepted (with qualifications) by the EU. However, the early consensus around creating a 'safety net' against the parties falling over the cliff-edge of a disorderly departure and a 'bridge' to a future relationship changed after the negotiations were concluded. For those opposed to the negotiated Withdrawal Agreement, the transition period – like the Irish 'backstop' – seemed more like a 'trap' or a 'trampoline' to maintain alignment with the EU post-Brexit. The first aim of this article is to analyse what the UK and the EU sought to achieve in the negotiations by agreeing a transition period. The second aim is to consider whether – in combination with other factors – the outcome of the negotiations on a transition period contributed to the failure of the UK to exit the EU as intended on 29 March 2019. The article concludes that the Article 50 negotiation process underestimates the way in which the momentous nature of a decision to leave the EU unleashes political forces that inhibit a smooth and orderly exit and transition.