You are not as experienced as you think you are.
I wish someone I respected had told me this when I was a college student. In college, I thought I was super-awesome. I thought I was already a leader. I thought I was qualified to manage a 100-person company. I thought I didn't have much else to learn; I just wanted to start a company so I could grow it and sell it and make a ton of money like everyone else.
Now I know that I am merely above-average and lucky. I know that for every problem I face, there is someone more experienced than I who has already solved that problem, thrice-over, and wants to help me. If I had known this 10 years ago, I think I would have sought out a lot more advice, been much more receptive to criticism, and been a better entrepreneur.
Note: obviously this is 100% personal and anecdotal. I may have been the only a-hole in college who needed to hear that message, so YMMV.