1. You didn't prepare well.
2. You never sold them on why you should work there. Which means you didn't prepare well.
3. You didn't know your resume and your background well.
(Yes, you need to remember the years you worked there. Saying, “It was long ago, I don’t remember” is a lazy response when you’re interviewing. You didn't prepare well.)
4. You did something like wear too much cologne/perfume, looked ill kept, had bad breath, wore the wrong thing or forgot your resume. Check the company's website for their corporate culture (how to dress) to learn how to fit in. Bring a resume. Again - you didn't prepare well.
- Got the hint? Prepare well. Know the company and know yourself! Sometimes the chemistry is just off - it happens - but if you found a great job at a great company that's a good fit and you blew the interview, it's because you didn't prepare well.
To learn how to prepare well check out this video from Dave.