The hard truth about job hunting is that the best job in the world may not be the right job for you.
After your write an excellent resume and cover letter, after you apply for that job that looks good on paper, after you research the company and complete your interview preparation, after you ace the interview -- then you need to know what you want out of the job, the bosses, the workplace, and the company. You need to be able to ask questions that will tell you whether the company's answers match up with what you need to be an excellent employee. And you need to have the strength to walk away if the answers don't match.
Conversely, you need to be ready to hear that you won't be getting the job. Because after you write and excellent resume and cover letter, and after you ace the interview, you may still not be the right person for the job based on any number of criteria that your interviewer can't quantify. Or you might be 99 percent right for the job, but another candidate is 102 percent right for the job.
In other words, it's all about fit.
It's difficult to determine whether a position will fit you when you have only an hour or so to talk with your potential boss. It's a bit like going on a blind date and getting married after dinner! Both you and the hiring manager are trying to make the best decision possible in a high-pressure situation, and much of it hangs on the intangible concept of fit. To a degree, "fit" is like pornography -- job seekers and hiring managers feel that they will "know it when they see it." And much like dating, sometimes the attraction is one-sided.
Job seekers, the best way to determine whether a job is the right fit for you is to listen to what your gut says. If you've done your research before the interview, and asked your important questions during the interview, then you have done all you can do on that score. The rest of it is in the hiring manager's hands. If the hiring manager determines that you're not the right fit for the job, believe it, and move on.