Two co-founders, no written agreement, and the company is now worth something

What we told them

Write it down now, while you still agree. The worst version of this conversation is the one you have after a disagreement, when every clause looks like an attack. Start from what you would both consider fair if you did not know which of you would want to leave first — that is the only frame that survives. Cover equity split, vesting from the original start date, what happens if one of you leaves, and who decides what. A short agreement you both sign this month beats a perfect one you never finish.