Tests are basically same as free climbers safety lines.

Absolutely. So many people seem to aggressively argue for 'test all the things!' or 'test nothing!', where I imagine most jobbing programmers are practical enough to test the key things first and then expand from there. If I'm greenfielding something, I'll do TDD-first, but on new features on an old code-base or legacy apps it's initially way more just a catch in case I come off the mountain unexpectedly. I don't want to spend a day writing a feature and then find out I've broken something fundamental, I want to find that out after a couple of hours.