It's a little-known secret — many Co-Founders typically quit in the first year.
We don't hear these stories because, by the time a startup becomes successful, they are long since written out of the annals of the company's history. If we're a first-time Founder, we don't realize that there's a massive delta between the commitments we make when we start a company and those that we have to maintain as the grind continues.
The problem becomes real when we realize we just gave our "forever committed partner" 50% of the company for what amounted to 5% of the long-term effort required to make it successful. If we had known Co-Founders don't last, we'd have prepared accordingly.
So why don't Co-Founders stick around?