Why People Die by Suicide by Thomas Joiner. It is not an easy read but helpful. Am re-posting this from 2007.
Joiner says people commit suicide because of thwarted effectiveness or the “sense that one is a burden” and thwarted connectedness or the “sense that one does not belong”.
A final necessary factor occurs when a person has acquired the ability for lethal self-injury. “This comes from fearlessness about confronting pain, injury and death.”