Is it when you graduate from college with a science degree?
Is it when you publish your first paper in a peer-reviewed journal?
Is it when you get your Masters? Your PhD?
Is it when you get your first job being paid to do science?
Is it when, as a professor of mine suggested, you have contributed more knowledge to science than you've consumed?
...
I was talking with a few friends (grad students all) about this, and we have some pretty varied opinions. Obviously, the professor's opinion above is rather extreme -- is it even possible to contribute more to science than the cumulative efforts of Newton, Darwin, Maxwell, Mendel, Euler, Einstein and the other geniuses whose ideas have been condensed down into the textbooks we've read?
Personally, I think being a scientist is a state of mind -- a way of interacting with and learning about the world. It's a spirit of curiosity, a drive to explore and observe, the humility to change even your most firmly-held ideas if the evidence contradicts them, and the notion that the strength of an idea lies in how well it fits observable facts. Ironically, grad school is sapping most of those qualities out of me -- but maybe that's just the stress talking

What do all you future (present?) scientists think?