At least two-thirds of suicides occur in people with major depression--in fact, some experts contend that all suicide is related to depression. Why do some people develop depression over and over, while others with similar life circumstances and experiences never do? Like everything else, the answer is genetics (and probably not one gene, but many genes, and the interaction of the environment with those genes). Some people are more genetically prone to depression, and therefore to suicide. It is not that likely that career choices and circumstances cause depression or suicide. It is much more likely that the same genetic characteristics that make a person prone to depression also make them more likely to choose certain career paths. Specific talents and interests may be genetically linked to a propensity for depression.
So now I will preach a little. The unfortunate truth is that our society frowns on and does not understand so-called "mental illness." I say so-called because it's my contention that all mental illnesses will ultimately be shown to be physical illnesses: that is, biochemical issues in the brain. Neuroscience is already well on its way in this direction, and more pieces are falling into place every year. Despite the fact that depression is a fairly well-understood biochemical phenomenon, the idea that the sufferer is weak is the last bastion of prejudice in our society. Most of us would not belittle someone because their pancreas does not make insulin or their thyroid does not make thyroid hormone. Somehow, in my lifetime, the disdain for alcoholics and drug addicts has completely turned around, and we now cheer on those who work to deal with their addiction by accepting treatment. I hope the same thing will happen with other "mental" illnesses.
Finally, if anyone here is feeling depressed or contemplating suicide, please get help.