Users soon stop using unreliable software if they have a choice and testing would seem to be the obvious fix for this; but testing costs money to do and even automated tests have to be maintained, so add to the overall costs of development. So the truth about testing is a lot more nuanced and has to be assessed in the context of the maturity and value of software system. The real truth is the any software testing needs to be strategic and that strategy must change according to the circumstances.
Judgement is one of the biggest things experienced product developers can bring to a team. This judgement can massively influence the costs and outcomes of any software project. Ash Winter recounted a recent experience surrounding testing strategy at Agile Yorkshire and points out what can happen when the costs of testing become misaligned with current business forces.