You have some control. Far less than the "suicide is selfish" idiocy assumes.
Great, maybe that's the case. However, there's no more evidence for that than the assertion that suicide is a choice.
That fits with my experience. I have to be very careful with peanut oil, for example. It does terrible things to me.
So, in short, it is possible that depression and other mental illness has biological roots. There are also social factors and other factors, but in some sense mental illness may well be a medical illness.