I still don’t know how to explain that in two minutes, but I can try to do my best here. That discussion has two aspects:

  • if you trying to get manual testers to test the same way as test automation does that you are not using them efficiently.
  • if you trying to get test automation to test the same way as manual testers do that you are not doing it right either.

So below some differences:

  • you wouldn’t want to repeat all manual tests on each change
  • you wouldn’t want to reproduce all checks manual tester do in test automation
  • you wouldn’t want manual testers to use curl when there is web UI or test web UI against mocked server
  • you usually would be more efficient when you do not script manual tester work the same formally as you do that with test code

There are really a lot more differences, but strictly speaking even list above is enough to demonstrate that they are different, and you cannot compare them one to one, calculate ROI and etc .