Not being able to make enough money. As I lived in extreme poverty in my childhood (and all that changed thanks to online MOOCs). I now work as remote SE and I have around $10k in savings. I am graduating with robotics and AI masters degree. But I always fear that I will lose all my money and be poor again. I literally prefer dying than being poor again. The worst days of my life, I couldn't have a proper childhood because of that, it's the thing that I fear the most in this life and haunts me everyday.