How to pick a co-founder?
What is a good co-founder worth?
Assume that you will execute your most ambitious vision for your startup. Are you willing to give half of those earnings away? For most entrepreneurs, it's a no-brainer yes.
With that in mind - who is your co-founder?
Ambitious outlier you found way before the world did.
Understandable, but very counter-intuitive-
We don't judge our co-founders as much as we should in the initial days of starting up. That reflects in our vetting process.
Co-founder choice problem is going to be heard more since more startups will be founded by people that have not known each other before starting up. After observing tense founder relations and analyzing personal failures on the topic, here are my thoughts.
Two things become important in finding a co-founder: complementary skills and opposites in values. It is easy to figure out and pair up with someone with complementary skills. And easy to say no to someone whose core values are radically opposite to yours. But what if their values are somewhere in-between?
Founders with different core values shouldn't startup together. Why? You won't work with the same enthusiasm as you should. And it will end up in divorce at one point or the other.
You want to find an ambitious outlier way before the world did. With the same core values as you have.
Actual core values are found three layers below what people say their core values are. Any core value expressed in a single word is marketing material/ dictionary content, not a core value. You can't have "honesty" as a core value.
Throughout your conversations, understand
What they say their core values are
What they actually do
Their past stories
Most of the core values are very personal and less professional. You want to ask deeply personal questions you are comfortable answering.
Some examples: If your co-founder says that they are a feminist (and probably is) but also has a knack for (and enjoys) cracking good sexist jokes that you don't have an appetite for - you have different core values. If your co-founder is getting angry and displaying it in a way that you are uncomfortable with, you have different core values (how much ever warranted it is and how less often it is).
Work together for a few days/weeks. That gives most data about each other. You are looking for someone who is smart(er) and puts in effort at the scale you aspire to be. The best co-founder choice is when you are intrigued by their intelligence and inspired by their effort levels. And it comes naturally to them.
Your productivity graph is your data on whether the team works. Even better - get an external party (mentors/friends) to track your productivity graph.
Confidence in the co-founder choice is like a hockey stick. The trick is to take just the right time to stay in the slow growth phase before shooting up.
Check if you are fighting the correct problems and facing the right failures. If the battles are about internal execution, you have a problem. Battles about external reception will be your day-to-day execution and are the crux of starting up anyway.
Check if you can have tough discussions and sustain failures (but also have a good smile about it later). Not being able to have tough discussions is a strong indicator of mismatch.
Check if you can celebrate the failures. It's easier and comes naturally to celebrate success. So ignore that data point, especially pseudo-successes like fundraising. Most of the startup journey is an uphill climb through luck valley. You will have harsher times than easier ones. You want to pick someone with whom you can enjoy even the harsher times.
And importantly, check if your collective assumed ambition is scarier than individual reach.
You want to find an ambitious outlier way before the world did. With the same core values as you have. With whom you can fight the aligned battles.
Co-founder choice is a one-time decision. Co-founder relation is continuous execution. Often, founders are too involved in day-to-day execution that they forget to give time to nurturing the relationship.
Talk 2x more about vision than you do now. Why? Day-to-day execution is so much farther from the long-term vision. This makes founders talk about long-term vision rarely with each other. You want to keep dreaming together.
The best co-founder relationship is when there's radical respect for each other. One way to achieve it is with radical transparency. Radical transparency can be achieved through radical communication.
Some examples: I know founders who had access to each other's email ids, so they could reply to customers immediately even if the other person was asleep. Some founders have special chat clients dedicated only to the co-founders. Both are assured that their messages won't get ignored by other notifications. Some chat and speak with their co-founders more than their partners/spouses. I know founders who didn't have much respect for each other's decisions and didn't have agreed-upon ways to deal with harder circumstances. As the team grew, employees noticed, and the employees lost respect for the co-founders. It's hard to earn it back.
Your co-founder's ambition is not-yet realized. They are going to make tons of mistakes to get there. You want a co-founder relationship where it's easier to make mistakes, and there's the confidence that you can learn from them.
Be okay with making a bad co-founder decision. It takes time to figure out what matters to you. Best to make a mistake and iterate than not starting up at all.
 If it works out, what difference does x$ vs 2x$ make in your earnings? With reasonable probability, x$ is a lot above your fuck-you money as much as 2x$ is. And for that difference, you get someone to climb the uphill with. Most startups fail, you might as well face the hurdle with another person. If your answer is not a yes for this (which I can imagine a second or third-time founder saying), then the rest of the essay might not make sense.
 My thesis is that being evolutionarily pessimistic, it is hard for us to imagine ourselves winning as much as we should. Whatever every entrepreneur aims for, they should aim way more than that to offset innate pessimism. Even the smartest and most ambitious entrepreneurs might not give a thumping yes when asked if they are the person who would achieve their most successful self. The difficulty gets amplified when you have to answer the same question for a co-founder since it requires double the confidence. Day-to-day startup execution doesn't help, either. A significant portion of time is spent on micro-level execution at MVP stages. And when you are doing anything and everything to make those small pieces fall in place, it is understandable that you don't match up yourself to what you should be, because when we think of our most ambitious and successful self, we rarely imagine ourselves doing what we do today.
 The constraint that founders should know each other before starting up produces limited startups. People investors/ accelerators like EF are entering the ecosystem to bring smart individuals together to start a startup. It's a win-win scenario for founders and the market. Deepti, my co-founder @Adaface, and I met at Entrepreneur First, Singapore batch for the first time, and we ended up starting up Adaface five months later.
 Naval has a good piece on this with better words and crisper sentences. https://nav.al/intelligence-energy-integrity
 Ask anyone you know if they are honest - almost everyone will agree. But we know that can't be true. Most people are not willingly dishonest, either. The scales of honesty are different, and we assume that everyone else works with our levels of openness. (we can replace openness here with any value word)
 It's very easy to think you are being productive just because you are putting in the effort. An external party asking the right questions and judging would be a better sounding board to see if you are actually being productive as a team. One of my favourite ways to think about this - your friends always see your breakup way before you do.