The phenomenon of “structural irrationality” covers a diverse range of combinations of attitudes, including (inter alia) contradictory beliefs, contradictory intentions, means–end incoherence, akratic incoherence, and cyclical preferences. This paper offers a novel, unified account of when a pattern of attitudes qualifies as structurally irrational. It begins by setting up the core of the view I will be defending: a set of attitudes is irrational if and only if it is impossible for those attitudes to be jointly successful. I show that this view can account for a wide range of paradigmatically irrational combinations of attitudes. I then refine the account to make it sufficiently subjective. I argue that a set of attitudes is irrational only if the impossibility of their joint success is (i) logically transparent, (ii) subjectively inferable, and (iii) not justifiably denied.