Optimism is an occupational hazard of programming; feedback is the treatment.
If testing costs more than not testing, then don't test.
I don't like the feeling, but I've got to say that a little fear makes me a more focused, more responsible programmer.
If you're having trouble succeeding, fail.
Testing is not the point. The point is about responsibility.
Responsible Development is the style of development I aspire to now. It can be summarized by answering the question, How would I develop if it were my money? I'm amazed how many theoretical arguments evaporate when faced with this question.