The fintech space is experiencing exponential growth, with the number of startups more than doubling over the past five years, and as a result, companies in this sector need to adopt product principles that can differentiate their platforms. To better understand these principles, three fast-growing fintech startups, Acctual, Basis, and Causal, shared their approaches to product development, including treating product usage behavior as the ultimate source of truth, adopting a systems-first mindset to build future-proof products, and providing seamless integrations to enhance customer experience. By prioritizing these principles and making necessary resource investments, fintech companies can effectively differentiate themselves in a crowded market and come out on top. The experiences of Acctual, Basis, and Causal demonstrate the importance of monitoring customer behavior, building scalable foundations, and offering API-based integrations to power financial models and drive business growth. Ultimately, the successful application of these product principles will be critical to the long-term success of fintech companies.