I've co-founded four companies now — ErasmusInn, Oval, Fullog, and Cendra. Each time, the co-founder dynamic was different. And each time, it was the single most important decision I made.
Complementary skills, shared values
The biggest mistake first-time founders make is partnering with people who think exactly like them. It feels comfortable, but it creates blind spots. At Cendra, my co-founders Mumin Sahin and Ali Ozaltin bring deep technical and product expertise. I bring the operator lens and commercial instinct. We overlap on values — urgency, ownership, honesty — but our skills are genuinely complementary.
Stress-test before you commit
You don't know someone until you've been under pressure together. Before formally co-founding, work on something together — even if it's small. See how they handle ambiguity, disagreement, and setbacks. The early days of a startup are relentlessly hard, and the wrong co-founder will make them impossible.
Aligned on sacrifice
Building a company requires real sacrifice — financial, personal, emotional. You need co-founders who are genuinely willing to make those sacrifices, not just say they are. Misaligned commitment is a slow poison. It doesn't kill the company overnight, but it creates resentment that compounds.
The ability to disagree well
The best co-founder relationships I've had are the ones where we can disagree openly, make a decision, and then commit fully — regardless of whose idea won. If you can't argue productively with your co-founder, you'll either avoid hard conversations or let them fester. Neither ends well.
Choose carefully. Everything else — the market, the product, the timing — can be iterated on. Your co-founders can't.