Why does the mad man go crazy in the short story The Diary Of A Madman?

Aksenty Ivanovich Poprishchin slowly descends into complete madness after experiencing a number of failures, particularly heartbreak. Poprishchin is unloved, treated poorly by those around him, and obsessed with the boss' daughter. Unfortunately, he lives in a world of smoke and mirrors where he deludes himself more and more as time passes. In the end, Poprishchin completely withdraws into the world where he is happiest..... an unreal world, albeit, a happy one.