Yep, boxes are challenging. At the end of the box challenge I mostly felt like only my line quality had improved. It takes a long time to remap how your brain works. I did 20-30 a day and rushed it, which I feel was part of my problem.

I'm sure others have come out with a feeling of more progress but 250 was only ever just a good first milestone. Nobody comes out at the end of the challenge with boxes mastered. Everybody has to keep boxes in their practice rotation to keep improving and to stay sharp.

Don't be disappointed in yourself. If nothing else, get satisfaction at completing a goal you set yourself. If it were an easy skill to acquire we wouldn't admire it like we do.

Here is some advice I have saved for myself from Jake Spicer's figure drawing book because I think they can help you going forward:

Be patient. Most people overestimate how much they'll improve in the first six months, but underestimate how good they can get in five years.

Date all your drawings and store them away, without looking at them too much. Return to them three months later. Regularly look at those three+ months drawings.

The strongest ones help boost confidence.

The weakest ones show you how far you've come.

The average of the drawings will help you gauge your progress.

Your best drawings will often stand out as better than anything else you make for a while.

Your very worst drawings will always be terrible - in fact, they'll often become worse as you get better and start to take more risks.

Again, it is your average drawings that you should use to measure improvement.