Philosophy
The Philosophy of Probability: Objective, Subjective, and Propensity Interpretations
Quick fact
The three main interpretations—objective, subjective, and propensity—pose very different answers to the same question, and philosophers of science still debate which is the 'correct' one. For instance, a frequentist sees the 50% as a long-run pattern, while a subjectivist sees it as a measure of your personal uncertainty.
Why this is interesting
What does it mean to say a coin has a 50% chance of landing heads? Is it a fact about the coin, a fact about your knowledge, or something else entirely?