At the beginning of my career.  The first two years were a bit tough.  I felt disoriented.  If someone has told me that this is normal, and to expect certain things early in the career, it might have been a smoother ride.  Early in my career, I wish someone told me that:

1. Theory does not apply in real life:  Unless you customize it to suit real situations, real people, and real organization.  Furthermore, what people apply in real life is only a small portion of what is taught in school and in ways that depend on the organizational culture and personal style.  Not on academic theory.
2. Ability to work with people is more important than technical skills.  How you say things matter more than what you say.
3. What you think will take a few days can actually take months: to be done in an organizational setup.  Politics, resistance, clashing working styles, and other human factors need time to change.  People are not machines and there is no “on-off” switch for them.  You need to work with people, understand them, relate to them, before you can influence them.
4. Compromise is not a bad word.  Sometimes you have to compromise.  Half a solution sometimes is better than no solution.
5. My boss is boss not because she has more technical knowledge, but because bosses know how to “manage” better than me.  And while I might think what they do is “basically nothing” they do a lot to ensure my success.
6.  Part of my job is to support my manager.  Work as part of the team, and even if I feel I have a better plan, to support my boss in how he thinks things need to be done.
7. I think I know a lot, but I do not. Some of the people I worked with used to jokingly say “what we have forgotten about project management is more than everything you know.”  I used to get agitated by such statements but now I know that what they said probably was true.  Especially that they were old geezers and forgot a lot.  Just kidding.  But seriously, I needed to pay more respect to experience and not try to get my way all the time.
8. Early Career is not about money.  If you get a good role where you can learn a lot from a good manager or a good process, that will be worth much more than any money you can get somewhere else where there is no learning.  Probably after year three, if you got years one and two right, you will start getting better offers.
9. Don’t stick around for longer than three years.  Some might not like this.  But especially in early career, you need to move to get a good promotion or better salary.  Be careful that staying for less than three years might not look good on your CV.  Also, three years is a good learning period.  Staying longer than three years and your experience might become repeating the previous years experience over and over.
10. This is the beginning.  Do not give up too easily too fast.  Do not rush wanting authority and power. You will get there.  Build a good career, thinking long term. Do not rush and enjoy every step.