The Broadway play that ex-Birdman Riggan Thomson is about to stage ends with the protagonist, played by Thomson, shooting himself in the head with a gun. And at the end of the actual premiere Riggan choses to use a real gun instead of a fake one and actually shoots himself in the head for real. Now it is still a bit debatable if he actually survived that act or not (as evident from those related questions), but the fact that he did shoot himself in reality and that he did this deliberately seems largely undenyable.
But why did he do that at all? What were his motivations for shooting himself and was this a rather short-term decision or did he plan this all along? Could he just not stand all the pressure that the play and its circumstances imposed on him anymore or was this just the ultimate commitment to his act? Or was it a total short-circuit reaction? Or did he just feel satisfied that he achieved what he wanted to achieve and the play was an ultimate farewell anyway?
The maybe/maybe-not real epilogue to me actually provided a nice satire on the whole authenticity-fuss (Boyhood anyone? ;-)) when it showed the universal praise he got from the critics for nearly killing himself on stage (even if that might not have been intended as a satire at all). So maybe he actually wanted nothing more than to provide an authentic act and saw this as his last chance to do so? But this isn't entirely clear and he seemed to a large degree unmoved by all this.
(Now of course the usual disclaimer that this whole question might have been intentionally left open, but even then I'm sure someone might find a satisfying theory, reasonably and objectively backed by the movie or other sources.)