I think the hardest thing I have come across in my career is gaining confidence in my self and the decisions I make.
At some point, you have to become the person who makes the decisions, not just contribute and let someone else make the choice. This is a big career moment, as it means you have grown in knowledge and experience.
My advice would be to always have good mentors, through school, university and your job. Having someone who is invested in you doing well and improving your skills will help your confidence massively!
Oh and studying my undergraduate degree whilst working 40+ hours is also quite difficult… but it is self inflicted difficulty!! Don’t let it put you off, it is also very rewarding and means I have no student loan!