Read on FreeCodeCamp.org:
What kind of graphic would capture someone's attention for a topic as mundane as SEO? The same way you can sell anything else—with a similar 3-letter word that starts with "S - E - _". Make it a letter-by-letter tease, then hit them with an O at the end!
Since I was writing about Google's search algorithm, I thought the art direction should be presented as if Google designed the graphics themselves: simple but easily understandable.