Dear sir I can understand your concern. As per Darwins hypothesis ..all living species ( including human ) follow 2 main principles * survival of fittest & * struggle for existence Now this struggle ll be throughout the life . What we have to learn is to stay stable , help others. Life is a matter of uncertainty and that is the real spice of it. Staying stable and managing all day to day activity huzzle  is also a type of intelligence. One should try to learn this as well . Existential crisis is bit common in struggling phase of life and serves as a fertile soil for anxiety and depression ( it depends on bio_psycho_social factors)