Yes I agree external conditions can harm you, but it's also true that the only thing you really have control over is yourself, your reactions, your actions, your inner dialogue, and so on. You aren't likely to be able to influence other people or events much.
I can say - if you can make it through a bad time, things do often get better - they did for me. If you are surrounded by toxic people find new people, and also if you are seeing someone for your mental health make sure you tell them what's going on.