For the other sciences it´s easy to point to the most important equations, inequalities, propositions or concepts that ground the discipline. If I want to explain Finance to a physicist say, what are considered to be the most important equations, inequalities, propositions or concepts that underly the subject which I should introduce and attempt to explain?

Above paraphrased from: Fundamental equations in economics

My guess would be the fundamental theorem of asset pricing or some Pricing Principle, but that's coming from a mathematical finance background. Would people coming from a corporate or personal finance (or whatever else finance is out there) background say something similar?