As a certified small keelboat skipper, I understand watercraft sails. I think I understand solar sails, but not nearly as well. I know Stephen Hawking wanted to send a bunch of micro drones to Alpha Centauri using solar sails powered by on-board lasers. That seems like the whole fan on a boat pointed at a sail situation, which doesn’t work on earth, so maybe I don’t actually understand solar sails. I’m definitely not going to say that Stephen Motherfucking Hawking was wrong about his area of expertise.

Edit: I got really curious about this after posting and looked into it more. The project was called The Breakthrough Starshot, and I misremembered the configuration. The lasers weren’t onboard the spacecraft, they would have been earth or satellite based. So I guess I do understand how solar sails work. When photons hit the sail, they impart some of their momentum to the sail, and the attached spacecraft. Since billions of photons are hitting the sail every second, all those tiny little pushes provide forward momentum. I’m still not sure if you can use a high efficiency propellant keel to sail towards the light source or not, but I’m thinking probably “no”.