I started collaborating with Sayan soon after joining Duke. I don’t even remember how it began—he just popped into my office one day and invited me to join a nearly finished paper. That was Sayan: always generous, always welcoming. He was someone I could turn to for help without pretense. He shared his grant proposals, promotion materials—things people usually guard—without me even asking, just because he thought I might need them.

A few days ago, I saw someone who looked like him at a coffee shop in San Francisco. For a brief moment, I thought, Could that be Sayan? Then came the next thought: No, it can never be him anymore.