The heart of all ethics is something which … has nothing to do with the register of ethics. This ‘something’ goes by several different names — for Lacan, it is ‘the Real’; for Badiou, ‘the event’. These terms concern something which appears only in the guise of the encounter, as something that ‘happens to us’, surprises us, throws us ‘out of joint’, because it always inscribes itself in a given continuity as a rupture, a break or an interruption. According to Lacan, the Real is impossible, and the fact that ‘it happens (to us)’ does not refute its basic ‘impossibility’: the Real happens to us (we encounter it) as impossible, as ‘the impossible thing’ that turns our symbolic universe upside down and leads to the reconfiguration of this universe. Hence the impossibility of the Real does not prevent it from having an effect in the realm of the possible. This is when ethics comes into play, in the question forced upon us by an encounter with the Real: will I act in conformity to what threw me ‘out of joint’, will I be ready to reformulate what has hitherto been the foundation of my existence? … For Lacan, the accent is to be placed, first, on desire (‘Have you acted in conformity with the desire which inhabits you?’), for it is desire that aims at the impossible, the Real.
Zupancic - The Ethics of the Real: Kant, Lacan. 2000, 235)