We learned many things. The two most important ones:
1. You can do more than you think. We came in wanting to grow into a 30 person company in 2020. Now we're 100+ people and plan to IPO in 2020. You realize that you have only so many years left and you want to make them count. And that with some help you can aim higher. Not every company should take VC and I love companies like Basecamp. But YC helped these two EU founders be more ambitious.
2. You can ship faster than you think. Seeing what is now https://www.wayup.com/ and other people in our group achieve much more than us every two weeks made us question how we worked. We learned to iterate and launch the minimal iteration as soon as possible. It was a counter-intuitive lesson that greatly increased how effective we are.