Your first product is always special. All the hard-work you have put and the struggles you had to go through, finally culminates into a tangible product that you are proud of. This question is a chance for everyone to learn from that experience and to hopefully prevent making some common mistakes. What did you struggle with the most - was it the team, design, the feature, customers, validation, marketing, scaling... ? and, what steps did you take that helped you to overcome it?