I know people who bought a computer and automated away a massive amount of work and thus paid it back in a single day in the 70s.

Back then companies needed a massive amount of people to sit and do all the calculations to do their accounting, but a single person using a computer could do the same work in a day. This was so easy and efficient that almost every bigger company started buying computers at the time.

You don't need to automate away accountants, you just need to automate away the many thousands of calculations needed to complete the accounting to save a massive amount of money. It wasn't hard to convince people to use a computer instead of sitting for weeks manually calculating sums on sheets.