(This post is part of a bigger list of rules that I have found helpful for thinking about a career, and beyond. See this post for an explainer).
There's a saying that I love: if you're the smartest person in the room, you're in the wrong room.
As much as you will grow professionally on your own, I strongly believe that a large part - perhaps even the largest part - of your growth will come from the people you are surrounded by.
One way to look at this is the following: imagine that you will become the average of the five people you are surrounded by the most. I don't think this way of thinking is too far away from the truth. As a consequence, if you are surrounded by people who are in some ways better than you, then that means that you will be able to learn a lot from them, and grow. The opposite is also true, hence the saying that if you are the smartest person in the room, you should really find another room.
This doesn't feel natural to most of us. It certainly doesn't feel natural to me. For most of us, the feeling of being the smartest person in the room gives us a cozy feeling; a feeling of being in control of the situation; a feeling that there is nothing to worry about. But in reality, you should actually be worried, because it means you are not growing as much as you could.
On the flip side, being the least smart person in the room can be quite painful (notice that I use smart here somewhat liberally, not necessarily to mean intelligent, but simply to be very good at something). In my experience, the ability to stand this pain is an extreme booster for anything you do. Whether it's personal development, scientific research, sports, arts: if you surround yourself with people who are better than you, you will grow.
When I was younger, I had a phase where I was ambitious enough to become a decent squash player. At some point, one of my work colleagues at the time invited me to go and play squash with him. Never in my life was I so humiliated doing sports. I did not stand a chance against this guy. Nevertheless, it became obvious very quickly that I had never learned faster, and more, than playing against him. By playing against someone who was better than me, again and again, my own game improved dramatically. And ironically, my aspirations of becoming a decent squash player eventually came true (that was a long time ago ;-).
Another mantra that is relevant here, and that I am sure you have heard many times before, is to get out of your comfort zone. The idea here is exactly the same: by challenging yourself - truly challenging yourself so that it feels uncomfortable - you will build the resilience and strength that is important for growth.
So don't be afraid to feel stupid. Feeling stupid is a sure sign that you are exposing yourself to things you don't know. Feeling stupid is an opportunity to learn. A great read in this regard is the timeless essay The importance of stupidity in scientific research.