I've had this puzzle on my phone for years. Every few months I'd glance at it and try and solve it. Last night, as I was eating dinner, I finally figured out the answer!

I’d like to ask the good people of this community that, if you do know the solution or figure it out, that you not share the answer here. Feel free to announce your success, but there’s something to be said for discovering the answer completely unaided, even if it takes years.

It’s embarrassingly obvious once you see it though.