[…]instead of aiming at Danny, it reversed the handle, aiming the hard side of the roque mallet at its own face. […] Then the mallet began to rise and descend, destroying the last of Jack Torrance's image. […] (55.76)
We are relieved Jack doesn't hit Danny with the mallet, but sincerely ache for Jack in this moment. We've come to sympathize with Jack by this point, and his self-inflicted violence speaks to the great anguish inside him. We know that at this point, there's little hope of Jack's survival.