Product-Market Fit
The holy grail: when customers love your product so much they tell everyone.
Explanation
Marc Andreessen defined product-market fit as being in a good market with a product that can satisfy that market. You know you have it when customers are pulling your product out of your hands faster than you can build it. Everything changes after PMF—growth becomes easier, hiring improves, fundraising flows. Before PMF, nothing else matters.
Real-World Example
Slack had PMF when teams started using it without IT approval and begged for company-wide licenses. Zoom had PMF when COVID hit and usage exploded because the product was already loved. Facebook had PMF when students stayed up all night using it. You'll know: usage grows without marketing spend, people get angry when the product is down.
How to Apply
Measure PMF signals: Net Promoter Score >50, organic growth rate, customer retention >90%. Sean Ellis test: Ask users 'How would you feel if you could no longer use this product?' >40% saying 'very disappointed' indicates PMF. Before PMF: iterate quickly, don't scale marketing. After PMF: hire fast, scale everything.