[RIP Bragi. You could probably substitute any other good wireless earbuds, though.]
This means I can learn and discover during activities where this was previously not possible.
Podcasts and audiobooks are available during commutes, flights, runs, bike rides, misc chores and errands etc.
The fact that they're entirely wireless, have very good noise cancellation (in-ear seal), a powerful touch interface, and are sweat/water proof, makes them especially useful. (e.g. skip song with double-tap while biking)
(Of course, use your discretion; shutting out the world and being always on the receiving end of information without time to process your own thoughts and letting them wander I think comes with a cost.)
Edit:
I'll echo what others have said as well: bikes!
Probably tied for first place is my bike which I bought off CraigsList in queens back in 2014. The decision to bike somewhere rather than driving/taking the train/walking means: new forms of exercise, new ways to discover a city, and it's fun :)
Oddly enough, learning Dvorak during a [slow] summer internship and then learning to use Vim regexes to edit/search a couple TCP dumps at my first job probably are the reasons I eventually became interested in scripting/programming and eventually a software developer.
Really if it weren't for the first challenge of learning Vim, I wouldn't have learned to program. Which, I know, sounds kind of backwards :P
IMO every wireless pair of buds I've seen released so far is a 'copy' of Bragi's Dash, and usually has only a subset of the features.
I still love my Dash Pros. Only downside with the experience is you can't pair to multiple devices. But the UX, the look, the in-ear seal, the sound quality -- all seem to me to be superior to anything that's hit the market, and they were designed ~6 years ago.
https://news.ycombinator.com/item?id=21362190