Totally pointless topic sadly as nobody replying can accurately answer unless they are in the very dark world that is clinical depression.

There are a couple of other states of mind that can trigger your mind to "allow" suicide, but by far the most common is the mind state known as clinical depression, a state that im sure 90% of so called "Off work with depression" sufferers have never even been CLOSE too IMO.

The rest of us, whilst reading this in a helthy state of mind will simply reply:
No way.
Cowards way out.
Selfish bastards.

Etc, as your current normal human mind state currently will not allow self destruction. You are still programmed first and foremost with fight or flight, as are most animals naturally.
people who take their own lives are FAR from the state of mind the majority of members reading ths topic are in, and until you have been there, you will simply never understand their reasoning.