I find the lack of measurable progress in writing to be frustrating.
Let me explain: I'm a professional musician. I also have a variety of hobbies that range from disc golf to beer making to archery. In pretty much every area except for writing, there are clear markers to tell you if you're improving or not.
Can you play the hard section that old piece more easily? What was your score at the end of 18 holes of golf? Did that batch of beer taste better than the last batch?
If you make a stout three times and each time it tastes better, you know you're doing something right. If your violin is making fewer glass-shattering squeaks, you know you're on the right track.
Writing doesn't have any markers like that. Sure, you find yourself more easily forming scenes or maybe your vocabulary has expanded or even your story lines more complex. But does that necessarily mean you're a better writer?
This problem is further compounded by the fact that older works usually sell better in the ebook world. They've been out for longer, more eyes have seen them and they've had more of a chance to trickle into the "customers also bought" sections on online bookstores. So even if your latest stories are better crafted, your older stories are more successful.
So how do I know if I'm on the right track or not?