Although he doesn't mention API Gateway in his list, I used to design AWS solutions for people, and it was by far the biggest mistake I saw them make cost-wise:

Although he doesn't mention API Gateway in his list, I used to design AWS solutions for people, and it was by far the biggest mistake I saw them make cost-wise: It can get scary-expensive in a hurry, especially if you aren't careful at your cloud architecture and really understand what all you'll be paying for.