There are a large number of reasons that can get someone to a place where they feel suicidal. Sometimes it can simply be a specific life event that gets a person so emotionally overwhelmed they do not feel they can face their rest of their life, and, on impulse, they try and kill themselves.
Appleby and Condonis (Hearing the cry: Suicide Prevention, 1990) wrote that the majority of individuals who commit suicide do not have a diagnosable mental illness. They are people just like you and I who at a particular time are feeling isolated, desperately unhappy and alone. Suicidal thoughts and actions may be the result of life's stresses and losses that the individual feels they just can't cope with.
For many others though, the seeds are sown well before the event itself, and in some cases, go back to childhood. Just being born in certain countries, of a certain race, or being of a certain age, may increase the suicide risk. These people have an above average propensity to commit suicide, but even in these cases it is likely there is some specific trigger for the suicide attempt itself.
The factors that increase suicide risk can be broadly broken down into three categories:
We also have more information on risk factors for the elderly and the young.