in reply to Winning people over to better development practises

When I gave a lunchtime talk evangelizing TDD (Test Driven Development), I summarised the benefits as follows:

Note that the first point above is the most important.

Update: Some further points added later from Effective Automated Testing:

The talk was well-received and did change both development practices and management awareness. I also illustrated each point with specific examples from our workplace (e.g. a developer refactoring without a test suite causing a rush of new bug reports from customers).

See also (update):

Updated 19-Mar-2006: Improved wording. Also note that many of the ideas for these bullet points were derived from chromatic and Schwern's excellent Test::Tutorial talk. See also Unit testing -- module, book, and website suggestions wanted. Updated 23-Aug-2018: Minor improvements to wording (keep in sync with Effective Automated Testing). See also You've gotta have tests! by talexb. July-2019: Added See also (update)