Both science and art. The breakdown:

Science (teachable)

Customer discovery frameworks, unit-economics math, pricing models, funnel analytics, A/B testing, legal structures, fundraising mechanics.

Art (judgment)

Reading markets early, picking the right co-founder, knowing when to pivot, recognising talent, sensing when a product is "done enough" to ship, timing the market.

The science is learnable in 6-12 months of deliberate practice. The art takes 5-10 years — and some people never fully develop it. Both matter; neither alone is sufficient.