As a humanities graduate who just read Superforecasting by Tetlock and Gardner, I was impressed and excited by Bayes' Theorem. I am also disappointed that I had never previously studied it, as it is a useful tool that I could have applied to many decisions involving prediction/uncertainty, i.e. almost regardless of my profession.
My question: what else am I missing? What areas of mathematics are useful to pretty much anyone trying to affect high-impact social change? I want to study them! I suspect there are other areas of probability I haven't encountered that can improve my decision-making, but I am also open to completely different topics.
I don't mind a bit of a slog, e.g. I am a computer programmer and started learning multivariable calculus when I became interested in neural networks. In other words, I'm not asking for easy maths (though I wouldn't mind it), I'm asking for widely applicable maths. Thank you!