One of the worst feelings for me is when I have no more opportunity to grow or be better at what I'm doing. In the case of being a designer this was apparent being the solo designer on a team.
This team was my first team of independent creatives all coming together on a per project basis. There was a lot I had to learn and still need to learn especially when it comes to this idea of process for dev handoff. But, as a designer you need feedback—multiple points and rounds of it. And not from anyone, while helpful, to me the most helpful feedback is from other designers.
This is where it takes two designers to help and grow each other's work.
For me it's gone from "I think this is good" to "I'm going to back my design" to now "ooooo let me keep cooking."
A good designer is like a good chef...
If there isn't another chef or sous chef in the kitchen then how do you really know if the dish tastes good. Another chef will challenge the taste and your skills to make a better dish. A server and customer will keep demanding the classics and settling for what they've known to be good.