Of all the opportunities to pursue in this life I had to choose one that gives me a great deal of unease. I have always been drawn more towards the straight answered questions and to those activities that give a definitive answer. Basically, I am very literal.
I can remember asking a question in regards to why Wayne Shorter played a particular note that didn't seem to fit the chord. The answer I was given? "Because he wanted to."
That's a hard answer to grasp when you are trying to deduce everything to a precise reason. There was no right or wrong.
Now let's consider the elements that create tension as a musician/educator. How about not having a definitive income, not knowing if you've just played your last gig (at least for a while), gathering a group of musicians to create music with and hopefully a bond, wondering if your list of items to practice is going to lead to the results you intend to gain, hoping your students practiced! Some even worry as to whether or not they will earn enough to pay rent, eat, support a family, etc.
Of course you can gain some perspective from past experience to formulate a plan in anticipation. You would be very wise to do so if you already have not.
Let's now consider the artistic endeavor itself. How do you measure your impact, the quality of your compositions, your ability to communicate with others through your music. Do you base it on the size of your audience ( which may be somewhat small if you are a Jazz musician)? Engagement of the audience? The feedback from other musicians? Maybe it's the list of critiques you receive on social media from those that could care less about your music but feel the need to comment.
Any and all of these answers may factor in to give the feeling of measurable success. On the other hand, maybe none of these answers give you the sense of being grounded. Maybe it's all subjective and immeasurable.