Fat gem mechanism is useful to install extension library without any compiler. Fat gem mechanism is especially helpful for Windows rubyists because Windows rubyists don't have compiler. But there are some downsides. For example, fat gem users can't use Ruby 2.7 (the latest Ruby) until fat gem developers release a new gem for Ruby 2.7. As of 2020, pros of fat gem mechanism is decreasing and cons of it is increasing. This talk describes the details of pros and cons of it then says thanks and goodbye to fat gem.