> If you spend 20% of your time fixing bugs and 80% of your time writing or rewriting features, tests are not the bottleneck; it's not an improvement to spend 5

> If you spend 20% of your time fixing bugs and 80% of your time writing or rewriting features, tests are not the bottleneck; it's not an improvement to spend 50% of your time writing & rewriting tests so you can avoid the 20% spent tracking down bugs. That is a good line of reasoning about when auto-tests are needed. However you did not take into account time that is required to discover that something is broken. Without tests you do not know if your code change breaks important features. So you should also consider how expensive it is to test your product after every code change. You do not have to test yourself and delegate testing to end users. But turning users into testers could be pretty expensive too (loosing potential customers). So auto-tests should be introduced much earlier than when you hit "50% maintenance" threshold.