Hydration. Eye-strain. Sleep. Exercise. Stress. Etc. https://en.wikipedia.org/wiki/Migraine#Cause
Meta: we seem obsessed about data and we have standard techniques for exploring relationships between them, but what is the equivalent source of techniques for first-principle root-cause search? (In the more practical, not the philosophical* sense)
* https://plato.stanford.edu/entries/causation-metaphysics/