Don't do it, measure progress instead. Measure where you were yesterday, where you were seven days ago, and where you were a month ago.
Write down all of the little achievements you make throughout the day to give yourself a sense of movement. At any moment, you'll be able to look back at what you've accomplished, and realize that, most likely, you are at a better place than you were last month, last week, or even yesterday.
In her book Mindset1, Carol S. Dweck explains how people with what she calls the growth mindset tend to find success. "Those with the growth mindset found success in doing their best, in learning and improving. And this is exactly what we find in the champions," Dweck tells us. "They knew that human qualities, such as intellectual skills, could be cultivated through effort. And that’s what they were doing—getting smarter. Not only weren’t they discouraged by failure, they didn’t even think they were failing. They thought they were learning." As a thought experiment, Dweck invites us to substitute "intellectual skills" for "artistic talent," "sports ability," or "business skill," and understand that those are not fixed qualities of our being, but something we can develop with deliberate practice.
Dweck shares the testimony of olympic athletes such as Jackie Joyner-Kersee, who mentions how "[she derives] just as much happiness from the process as from the results," or Tiger Woods, who "loves to win," but focuses on giving the most out of himself, even if he does not win. Most so-called "successful" athletes appear to find joy not in winning but on improving, on the idea "that personal success is when you work your hardest to become your best." This is why keeping track of your work can help you stay on track, as a way to visualize your effort and progress over time, and to realize that you are trying your best.
I keep track of my process inside of a digital folder named work-log: A folder to save screenshots and pictures of the things I get done throughout my day as I work on them, making sure I add the date of my "achievement" in front of the filename. (This is, something like 2018.06.26 or 180626 in front of the name of your files.) The work-log is a visual log that captures your efforts and improvements along your process with key snapshots of your work—a log you can browse to see the steps you took over the last days, weeks, or months.
For each large project, I create a separate work-log folder inside the project's folder to track the progress of the project itself in more detail, and only add key snapshots of that project to the main work-log.
If this manual process of taking screenshots and pictures sounds tedious, stick to adding the date in front of the name of digital files as you create them—you'll still be able to query your file system's search bar with a date to obtain the list of files you worked on that given day.
To summarize, I would encourage you to keep in mind that skill can be cultivated with effort, that personal success is trying your best and improving, without obsessing with results, and that you can benefit from keeping a work-log of achievements to visualize your progress. As Seth Godin puts it, "It might take seven years for a fast-moving internet company to become an overnight success2."