[Clubber]

It's a matter of cost. Adding good covering unit tests basically doubles your development time. You are paying now for dividends later.

In terms of business, you are trying to prove your business model. If your business model is bad, it doesn't matter how well your software is written. You need to prove your business model before you run out of funds.

It's a give and take. You really need to understand both the technical aspects and the business aspects to understand why entities might do certain things.

Also, people have been writing software without unit tests for decades.