"I wish I knew that sooner."
If you've run a company, you've sure said this before!
It's not that we regret our experience, but that our lessons learned came at a high cost. We know better, but in hindsight.
In too many cases, we took too long to launch, learned where we went wrong, but didn't have enough time left for another try.
This is why the ideal of launch fast and iterate is so valuable. By launching, we expose the information we didn't know, and didn't know we needed to know. We didn't know that customers only cared about certain features, or that the trick to getting sign-off is to keep each invoice under £50k, or that the design wasn't dust-proof enough for the customers' environment.
As founders, our job is collecting this useful and actionable information as quickly as possible. Getting that information faster means we make fewer uninformed decisions. The more frequently we get the right information, the better our decisions become.
Launch fast and iterate. Give yourself the benefit of hindsight sooner.