Culminating with the Quebec Secession Reference (1998), the Supreme Court of Canada identified several unwritten principles that it described as the ‘lifeblood’ of the Constitution – they ‘infuse our Constitution,’ they wrote, and ‘breathe life into it.’ Having a ‘powerful normative force,’ they even could give rise to ‘substantive legal obligations.’ Since then, the Court has curiously retreated from this stance, preferring to rely on the written constitution and declining to consider unwritten constitutional principles. This trend line was most clearly on display in Quebec v. Canada (2015), where the Court resisted having the unwritten constitutional principle of cooperative federalism constrain exercises of unilateral federal authority. Significantly, the three civil law justices from Quebec jointly issued dissenting reasons, having the support of several scholars from within Quebec. The Court’s behaviour indicates that the justices were not serious about the role of unwritten constitutional principles going forward. The chapter argues that the unwritten constitution was developed in the Secession Reference as a response to legitimacy concerns then facing the Court, which are no longer present. Judges and scholars from Quebec mistook these signals as genuinely novel developments rather than strategic responses designed to get the Court out of a jam.