First off, there are external circumstances outside our control: Some idiot may ram your car, extreme weather may destroy your house, economic turmoil may wipe out your job, war or civil war may end the illusion of stability and civilization in which you function so elegantly.
Then there is your own body, a less loyal servant than you might imagine. From one day to another, illness may strike, or even an accident. Falling down stairs, even slipping on a banana peel, could change your life forever. Even without that, a blood clot may suddenly hit your brain, or a rare mutation may already be at work inside you.
But even your soul is unlikely to be a perfect tool. Recently we have come to learn that ordinary humans have several separate "hot states" such as anger, fear and lust, as well as their normal somewhat rational "cold state". Once you enter a hot state, much of your soul is swapped out and replaced with a different persona. These are generally less alike to you than brothers and sisters. Most notably, promises made by one persona is unlikely to be honored by the other. I'm not talking about crazy people here, but the supposedly normal worker and parent, the respectable citizen (and politician, as most of you may have noticed).
Being a member of a certain social class or ethnic group or religion will not in itself change this fundamental structural flaw. The only known way to diminish it over time is by relentless self-observation and a death penalty to the countless excuses that bubble up to try to glue the personae together into one perfect person in our memory. "I deserve better", "she dressed like a **", "the idiot in the car in front of me suddenly braked", "a snake told me to eat it". As long as we allow these repair workers to scuttle all over our self image, we will never know who or even what we really are.
The truth is not for people with a family history of mental illness. It is better to sleep in the delusions that normal people consider reality, unless you have very little to lose and a family history of happy, laid-back sanity. For this reason, there are fairly few people in the world at any one time who are even looking in the direction of reality. The rest live on in the shadowy consensus reality of imaginary self control, where the world and the self are reliable and any exceptions are quickly forgotten.