Running errands. Waiting in line. Waiting for a train, bus, or flight. Commuting. Driving in your car.
Dead time.
There's a lot of dead time, you might not even realize how much there is. If you can fill this time up with valuable things, you're going to have a much better life.
I used to try bringing a book with me for dead time, and it works sometimes. Now I listen to audio, which can be done pretty much anywhere. Waiting in line at an airport? Audio. Commuting? Audio. Getting groceries? Audio.
I can't stress enough how big of a difference this makes. Fill up the dead time. There's lots of it. You'll be amazed at all you can learn in the time that's normally slipping through the cracks.