One of the most important lessons in The Perks of Being a Wallflower is that even during the darkest moments, human beings are capable of finding love.
Charlie is immersed in emotional darkness. Suppressing the memories of the abuse he suffered at the hands of his aunt, struggling with his friend's suicide, and experiencing the overall difficulty intrinsic to adolescence are all elements in Charlie's life that represent the darkest of moments. These events can block hope in the future. It becomes very difficult to see a bright future when the present is shrouded in such sadness and hurt.
However, the book teaches us that life has a restorative capacity within it. Charlie concludes his bildungsroman with the idea that "Even if we don't have the power to choose where we come from, we can still choose where we go from there." Charlie's words remind us that the human spirit is essentially an optimistic one. He seeks to make his life better. While there will be struggle and pain, he is not closing off the redemption that is a part of human identity. The book teaches us to not embody the sum total of what hurts us, but rather embrace the possibilities of what can be.