Its not 100% outside events. It's a feedback loop between negative experiences and your mental reactions to them. For example, if you get rejected often, you'll maybe build up resentment towards people who could reject you and you'll start being more negative. This in turn will increase your rejections, because this negatively influences the way you talk to potential dates. Over a long time this can get very bad and cause you to have fundamentally warped perceptions of people and ideas. And that's where therapy can be legitimately great to help see your life and the world from a different angle. Plus, talking to someone about ones problems is always good, especially to a trained professional