We prove Tsirelson's conjecture that any scaling limit of the critical planar percolation is a black noise.
(O. Schramm and S. Smirnov, "On the scaling limits of planar percolation", from the abstract.)

When conjecturing it (but only for the scaling limit whose existence was famously proved by S. Smirnov in 2001) I wrote "It would be the most important example of a black noise!" (B. Tsirelson, "Scaling limit, noise, stability", 2004, Sect. 8). I realized that my understanding of percolation was insufficient for solving the problem, but I did not realize the degree of difficulty of this problem. The brilliant solution was found by the two pioneers, leading experts, several years later.