Whether you are an astronomer or a life scientist, geophysicist, or a pilot, you've got to be there because you believe you are good in your field, and you can contribute, not because you are going to get a lot of fame or whatever when you get back.

This quote means that people should pursue a job or career because they are interested in it and believe they can do a good job, not because they will become famous or get a lot of recognition if they are successful. The quote is suggesting that people should enjoy their job or career and be passionate about it, not just seek a job or career because of the rewards.