Weekends puzzles are generally more difficult as people have more time available on those days.
There’s occasional drops in difficulty to prevent burnout.
Hard puzzles are sometimes introduced earlier as people are more likely to give it a try at Day 5 rather than something like Day 20.
Teach Yourself Programming in Ten Years | Peter Norvig - Research shows it takes 10,000 hours, maybe even 10 years, to become an expert in something. We can develop expertise through deliberate practice, connecting with other programmers, learning other languages, working on systems where no other expert for that system is around, and more
The Ultimate Deliberate Practice Guide: How to Be the Best | fs.blog - Deliberate practice is key to building expertise. It starts with identifying what specific aspect we want to improve, practicing with the intent of improving that thing, and then getting feedback either through a coach or through metrics to determine whether we are getting better at it.