Clearly every lesson is hard won from many years experience.
This is where development employment ends up I think after gaining significant experience.
You start by caring, making mistakes, throwing yourself into it, becoming disappointed, mad, excited, frustrated, overjoyed, deeply engaged, loving the company, less loving the company - believing in the mission.
Over time, you think about and wonder about situations that do not play out well, you formulate strategies to do better on them.
In the end, the passion for the company and its mission gives way to a cooler, calmer, more professional and reliable approach. At this point you're probably a much better and more valuable employee, but inside you no longer really care about what you are doing. You're easier to get along with, more predictable, and likely a very much better developer than when you started.
I'd say the employees who have learned all these lessons are the most valuable, but they're not going to be wildly enthusiastic perhaps. Unless of course the situation demands overt enthusiasm, in which case these employees might show the required enthusiasm, but it's ticking off an internal box "enthusiasm required in this situation".
I personally got to the point that I don't believe in any company mission except my own mission to make my own software - I'll build stuff for some other company, and I won't say out loud what I think about the mission/the product/the management/the strategy, but inside I won't believe.