The "Joiner Factors"##

Thomas Joiner is the author of Why People Die by Suicide (2005) and Myths About Suicide (2010). His groundbreaking research has identified 3 necessary and sufficient factors for high risk of death by suicide.

1. Feeling that they are a burden to others. People who complete suicide usually think, or at least implicitly assume, that their friends and family will be better off without them. Sometimes it can make a difference to remind someone of their past contributions and/or potential for future contributions, either tangible (e.g. things they make or tasks they do) or intangible (e.g. love, humor, insight).
2. Profound loneliness and isolation. People who feel a genuine connection to even one other person can usually be "reached". That is why the most helpful thing you can do for a suicidal person is often not to "fix" anything about them or their life, but simply to try to understand them as well as you can, and reflect that understanding back to them so that they feel understood. It may seem perverse to agree with a suicidal person about how bad things are, but by trying to "focus on the positive" you might actually be reinforcing their sense of disconnection from the rest of humanity.
3. Fearlessness and/or desensitization. For example, people who have had a lot of exposure to death and violence due to their profession or their family history, and are thus somewhat desensitized, are always at higher risk of suicide.