What is the most important lesson you can share as a founder about scaling a successful business?

I am a founder or co-founder of various start-ups, and I am hoping we can make this an informative thread of people sharing their valuable experiences. I will go first. As weird as it sounds I think it is really important you try to have fun! Start-ups are a tough process where you constantly feel under pressure, it is easy to get overwhelmed and burnt out. Trying to keep a positive frame of mind and trying your best to enjoy the journey help keep you mentally in check and on track!