> Software, as an industry, generally profits the most when it can identify an existing need that is currently solved without computers, and then make it 10x+ more efficient by applying computers. In this situation, the software doesn't need to be bug-free, it doesn't need to do everything, it just needs to work better than a human can.
Unfortunately, the project isn't "finished" after you achieve initial success. You have to maintain it for years after that. Without good tests, you get yourself into a state where one change breaks two things. You need teams of people manually checking it still works. It takes them an order of magnitude longer to check than it would take a computer. Your feedback loop that answers the question, "does it still work?" is in weeks instead of minutes.
You stop changing the bad code because it's too scary and dangerous. The bad code reduces the frequency at which you release new features. You slow to a crawl. The team of people testing gets expensive and eats into your profits. Some competitor eats your lunch.
In my experience, these problems occur earlier than you expect. Usually before you even attain success. I'm too lazy to comb over my app checking for bugs every time I develop a new feature. I get bored too easily to check that the same bug doesn't crop up over and over again. I'm also too impatient to wait for another person to do it. In these conditions, TDD speeds you up.
I've never worked on a manually tested project that avoided these problems. It usually happens around month 2 and gets even worse as time goes on.
Here's why I think TDD fails: The consultants say, "it's so easy! Just red-green-refactor!" No, it's extremely complex and difficult, actually. There's a ton of depth that nobody talks about because they're trying to get you to try it. The typical dev learns about "Just red-green-refactor" and fails. Now "TDD did not live up to expectations".
For example, did you know there's different styles of TDD? The author of this article doesn't seem to (I may be wrong, but he gives no indication). He's talking about Detroit style TDD (also known as classicist). This is the style Ron Jeffries, Uncle Bob, Martin Fowler, Kent Beck, etc. practice and advocate for. There's another style called London style (AKA mockist) that Gary Bernhardt, etc. practice. And then there's Discovery Testing from Justin Searls. There's probably others I haven't heard of yet.
They all have different pros and cons and a very common pitfall is to use a style in a way it's not really meant for. e.g., Using mockist to gain confidence your high level features work. Expecting classicist to help you drive out good design for your code.
To wrap this up, there's so much unknown unknowns about TDD it's usually premature to judge the technique. If you haven't tried all these styles, one might click with you. A lot of people are concluding they hate all sports when they've only tried baseball.