I disagree, and this is the mistake I made earlier in my career. Having the market is most important. I have built great products that flopped and ok products that were incredibly successful.

Quoting Andy Rachleff: If your startup addresses a market that really wants your product, you can screw almost everything up and still likely be successful. On the flip side, if you are really good at execution, but the “dogs aren’t eating the dog food”, you have no chance at winning.

“When a great team meets a lousy market, market wins. When a lousy team meets a great market, market wins. When a great team meets a great market, something special happens.”

It sounds more like we agree. "Having a market" and "The ability to reach people who have the problem my software solves" aren't so different.

But while "people who have a problem" equals a market, it's nothing if you cannot reach them.

The three of them form a triangle. Which side of the triangle is most important?

This is not a magical thing. Id argue it is fairly mechanical. The biggest issue you'd face is fear. Focus first on conquering that.

I think they're all necessary.

Product + grinding - building it and nobody comes, will get there eventually. Easier to learn to sell than to make a good product.

Sales + grinding - selling a turd, hopefully will get there. Harder to learn how to make a good product than sell.

Product + sales - flame out early