AppSumo promotion definitely played a role, but if I had to pick just 1 thing behind getting to 10k customers, this wouldn't be AppSumo. Furthermore, this wouldn't be any one thing.

...but if you had to pick one thing, what would it be? Curiosity abounds.

Context; I've been a paying PipeDrive customer for a couple years. Not sure how I originally was exposed to the product, (not appsumo), but I've stayed because the of the product.

One thing in addition to the product? The hustle in the beginning to get the product in the hands of the right people. Appsumo was part of it, but not a very big part of it compared to hundreds of hours that founders spent in pitching and "doing things that don't scale".