Suicide Prevention and Awareness

It seems as though we have lost numerous celebrities and public figures to suicide. It is easy to negate feelings of depression in instances like this because from our perspective, they have so much going for them. We see the fame, money, popularity, etc., and often struggle to understand why someone in their shoes would take their own life. The aftermath usually includes friends and family stating that they didn’t really know that anything was going on; maybe the person was a bit withdrawn, or busy, or maybe they started using drugs again that they had previously given up, or maybe they were on drugs and this was simply a part of their norm in that part of their life.
A suicide attempt is an act of hopelessness. The person feels as though the people around them may be better off without them, or they feel that they simply cannot get out of the situation that they are in.
What are some key signs that one could look for in their friends to try and prevent suicide? How open are you and your friends and family, when it comes to feelings of depression? Why is it important to talk about these things?