What was, in your opinion, the best baby-steps answer in 2016?
A baby-steps answer starts from simple principles and finishes with a complex and rich result.
Vote either by posting a link to your favorite baby-steps answer, with a brief description of why it's your favorite, or by upvoting an existing post. Voting lasts two weeks, i.e. until Jan 29 2017.
This is part of the Best-of PSE 2016. If you are interested in providing a prize bounty for the winner (mostly highly upvoted answer of this meta post), please comment.