In some of my interactions with undergraduates who wish to make a career in science I observe unrealistic expectations about what is required to survive, let alone succeed. Here are three lies they have been told and some have believed.
1. You are special.
If you grew up in the Western world you are part of Gen Y and it is likely you have been continually told you are wonderful and you can be anything you want to be.
Furthermore, if you are moderately bright and enthusiastic about science you may have received a lot of affirmation from high school teachers, career counselors, some peers, and/or undergraduate advisors.
This is particularly true if you attend an average or mediocre institution that desperately wants to recruit students to go to graduate school.
The problem is that once you get to a respectable graduate school you will discover that you are just average. Why does this matter?
Don't expect or demand special treatment.
You are going to have to work much harder than you have so far to get anywhere.
Aside: I found it interesting that in the popular book/blog Adulting the twenty-something author considers "accept that you are not special" is one of the key (and most difficult) steps to adulthood.
[I thank my own special adult children for bringing the book and blog to my attention].
2. Society wants you to become a scientist. We need more scientists.
Society does want this in principle, just not in practice.
Society is unwilling to pay for the high financial cost of supporting basic long-term research and the associated career structures. This means your scientific career will probably stall and end at the post-doctoral stage.
Consider the simple statistics. For example, the huge ratio of the number of physics Ph.D graduates each year in the USA to the number of advertised faculty positions at research universities.
3. You can have it all.
High grades, summer research projects, social life, international vacations, romantic relationships, the latest electronic toys, a car, a part-time job, hobbies, ... If you are going to excel/survive in science you are going to have to focus, set priorities, and make sacrifices.
I am not saying you should have no life outside of science. That is both unhealthy and boring.