Had a Jane Street interview in 2013 that still bothers me.
It was my 6th round. Final interview. The guy walks in carrying no laptop, no notebook, just a cold brew and what I later realized was a single IKEA tea candle.
He writes on the whiteboard:
food: $200
rent: $800
utilities: $150
candles: $3,600
family: dying
Then he turns around and says, âOptimize.â
I laughed because I thought it was a culture-fit bit. He did not laugh.
So I said, âWell, obviously you spend less on candles.â
He says, âAssume candles are non-discretionary.â
Okay.
I start building a model. Basic constraint satisfaction. Family survival as a soft penalty. Candles as a state variable. Maybe thereâs an arbitrage where you buy wholesale paraffin and convert the $3,600 line item into inventory.
He stops me.
âYouâre thinking like a consultant.â
Thatâs when I knew I was in trouble.
He says, âGive me a bid-ask on family dying.â
I say, âWhat?â
He says, âYouâre long candles, short family. Where do you make markets?â
I try to recover. I say the real issue is liquidity: rent and utilities are fixed, food is elastic, candles are emotionally inelastic. Therefore the optimal strategy is to securitize future candle enjoyment and borrow against it.
He nods for the first time.
Then he asks, âWhat time do you sell the candles?â
I say, âWhenever the market is liquid?â
He says, âBe more specific.â
I say, âUh⌠10 a.m. Eastern?â
For the first time, he smiles.
He goes, âEvery day?â
I say, âEvery day.â
He says, âIn size?â
I say, âIn size.â
He says, âAnd what do we call that?â
I say, âMarket manipulation?â
The room gets very quiet.
He looks disappointed and writes something down.
âNo. We call it providing liquidity to candle ETFs during the U.S. cash open.â
I try to save it. âRight. Of course. The family isnât dying because we underfunded them. Theyâre just experiencing temporary price discovery.â
He nods again.
Then he points back at the board.
I had missed it. The utility bill was $150, but candles provide light. You can zero out utilities.
I update the budget:
food: $200
rent: $800
utilities: $0
candles: $3,750
family: still dying, but now in a more capital-efficient way
He says, âHow confident are you?â
I say, â0.95.â
He smiles and circles candles.
â0.95 huh?â
Then he asks me to estimate how many leveraged longs get liquidated if we dump $3,750 of candles at 10:00:01 every morning for 90 consecutive trading days.
Needless to say I did not get the offer.
Jane Street made ~$40B in 2025 with 3,500 employees, a ~2x from the year before.
At ~65-70% profit margin, that's $8M profit / employee, the highest for a 1000 ppl company. High-frequency trading continues to be the most efficient money making engine.
I want to share an old story about my Jane Street interview in 2014. Jane Street was known for hiring a lot of math, physics and CS olympiad winners from top universities and putting them through many rounds - including, for trading roles, a gauntlet of mental math. It was my 6th interview and my final round and I recall being asked "What is the next day after today in DD/MM/YYYY where all the digits are unique?" They'd toy with you and say "You can use a pencil and paper, if you want" but you knew that was an instant no. Painstakingly and as quickly as I could, I came to an answer. "How confident are you that this is correct on a 0-1 probability scale?" the interviewer said. "0.95", I blurted out, not fully knowing how to answer that. "Are you sure?" After thinking harder for a few more seconds, I realized I could've flipped the digits around to get a closer date. I gave the interviewer my answer. It was correct. "0.95 huh?" he chuckled. That's when I knew I failed.
Note: fwiw, other companies that come close in efficiency are
- Tether ($90M profit/emp)
- Hyperliquid ($80M profit/emp)
and on revenue:
- Valve ($50M/emp)
- OnlyFans ($37M/emp)
- Craigslist ($14M/emp)
- Anthropic ($12M/emp, run rate)
- OpenAI ($8M/emp, run rate)
For comparison, Nvidia is very efficient at scale and is $4.4M/emp.