Just to offer a balancing point or two to the "my career teacher tried to kill my dreams" posts.
Firstly, the comments from successful Musicians, footballers, astronauts who were told they couldn't do it etc suffer from selection bias. Those people are maybe more likely to comment.
Second, I think it is OK for a careers advisor, along with helping you to find the route to your desired career, to also give you information about success rates and so on. All part of making an informed choice.
Personally, I didn't have a clue what I wanted to do, but eventually drifted into what suited me.