It's really good to study the classic writeup on product market fit. Although I tend to side with Shreyas Doshi that PMF is something that evolves and is not binary
Description
An extremely useful concept that has grown popular among startup founders is what eminent entrepreneur and investor Marc Andreessen calls “product/market fit”, which he defines as “being in a good market with a product that can satisfy that market”. Andreessen argues persuasively that product/market fit is “the only thing that matters for a new startup” and that ”the life of any startup can be divided into two parts: before product/market fit and after product/market fit.”