By the way, "spent almost 3 months on a 3 line tax calculation in a checkout flow" sounds about right. You say it yourself "had to work on several continents an

By the way, "spent almost 3 months on a 3 line tax calculation in a checkout flow" sounds about right. You say it yourself "had to work on several continents and query a silly amount of internal java services". A problem in the scale of a giant company like Amazon is a different problem altogether. Getting these 3 lines wrong could have, I suppose, catastrophic impact so spending 3 months on it makes total sense for Amazon.