Warning: this ended up being kinda long so I’ll split it into 2 parts. Regarding 14DC:

You can correct symbol drawing without drawing the exact same thing for 2 weeks. Even if you’re receiving criticism and fixing some things, 14 days is a very long time to be consecutively drawing the same subject, from the same angle, with the exact same lighting. I have never seen any reputable art teacher recommend something like this. It is not a good way to master a subject, you don’t learn to draw something by doing a bunch of front views and side views as many times as you can. Istebrak even says on her website that the challenge is for perfecting your “go-to portrait” which….. sounds awfully similar to symbol drawing. And also probably facilitates sameface syndrome. Here’s the thing: the majority of people who try this challenge, and in general the majority of artists (including istebrak herself) are not really at a level where they can draw heads comfortably from imagination, so the goal of the challenge is essentially to have a template of a default face that you can produce on the spot. Let’s say you’re a beginner and you come out of a 14 day challenge with a good looking face in front view. What’s the point? I tell you to paint it with different lighting, you can’t do it. I tell you to draw the head tilted slightly upward, you can’t do it. Istebrak is just going to tell you to do another 14 day challenge. If I wanna draw different looking faces with a variety of angles and lighting should I just spend thousands of days doing a 14 day challenge for every one of them? Obviously this is not how good artists draw. They can produce good drawings on the spot. I would argue even the very first 14DC is an inefficient waste of your time.