An interview is where you both (you and your interviewer) find out if you are a good match for each other. OK, not personally the interviewer, but the Company and job she/he represents. That is all.
If you are a good match, you will enjoy working there, you will make progress and will last. If you are not, it will be hard, you will probably not be appreciated, will not get promoted and at worst… it will last!

So there is no really a need to be overly nervous. Be yourself, act natural, be confident. If the job is not for you, the Hiring Manager will recognize it and, since you are being honest, he will keep you in mind for any job in that Company that requires the skills, experience and personality that you possess.
The other side is also true. Find out about the Company and decide if that is the place where you want to go, day after day, month after month and year after year. If it is, you will likely make great contributions, have a career, make a good income and enjoy your life. If it is not, show gratitude for the time spent explaining the Company to you, and move on with your search for the right place for you.
Remember that the worst job is the one you don’t enjoy, but pays well. A golden prison is still a prison.