In his continuing concern about the inevitability of automation, the very insightful CGP Grey provides an animated explanation about machine learning. Using very comprehensible examples, he essentially boils the subject down to bots making bots that use humans to learn, improve and eventually become smarter than the person who wrote the code.
But with machines that learn, we are increasingly in a position where we use tools or are used by tools that no one, not even their creators understand. We can only hope to guide them with the tests we make and we need to get comfortable with that, as our algorithmic bot buddies are all around and not going anywhere.
In a footnote piece, Grey describes machine learning in linear fashion.