What do you think is the most important factor in the success of a product?

Imo, the number of pain points it solves.

Product Market Fit

I will say something unorthodox; community and timing. Team and hardwork can be crucial for startups but if we are talking about success of an individual product i will say a community and being there at right time when there are people who needs your product.

In my opinion, understanding and meeting the needs of your target audience is key to the success of a product.

The value it gives to users must be true to reality and clear

First of all, it must solve some sort of problems and there should definitely be a demand for it in the market. Also, it must be very competitive in terms of pricing. High quality and reliability of the product improves retention drastically.

I think there are more than just one that I can't just say "most important" for success. But I would say timing is a pretty large part of it

Understanding the core problem/challenge and create better user experience, combining with a great ui.

Timing.

Sales