Limiting his horizons

I know, I really do know, that as a parent I should not limit my child's horizons by telling him what he should not set his sites on in terms of a future career.  But today I did.  It's just that we were in the car and when Theo gets in an enclosed space he tends to start to move.  Faster and faster- his little body seeking out anything that he can sense would not like to be bothered right then.  Usually this is limited to his brother.  But today he was even reaching up between the seats and bugging me.  I was thinking about how small spaces and Theo do not mix and before I knew it I had gone and told him that I really hoped he never considered a career as a submarine crew member.  Just picturing him there in those cramped corners with so many others- I know that it would get ugly, and fast.  And after I told him I thought he should avoid this he was actually quite crushed, like this was just the career he had been thinking about and I had dashed all hope.  Feeling bad, but really, it's for his own good.