After documenting his own progress, making it to 9d on Fox, Nate Moss has featured a student on his Telegraph Go Youtube channel. The student, going by the nickname "Sleep", has progressed from 15k to 1d in 3 years. A few takeaways from the video:

Nate's summarized advice along the track was to
1) emphasize strength and running battles
2) learn to read properly and apply it to fights and battles
3) look at the whole board and find surprising ideas throughout

My translation of that in high level concepts is
1) fundamental strategy/technique
2) reading; tsumego
3) whole board thinking; tesuji

It seems "Sleep" became rather obsessed with tsumego, solving more than 80K of them on 101weiqi.com. Nate has tried talking him out of that, trying to shift the focus to more effective aspects of the learning, but in the end it was a kind of intrinsic motivation, so there was no point of discouraging that.

Sleep took 60 lessons with Nate, which at a rate of - guessing 50$ - is quite an investment of time and money. In the interview, you can also hear how Sleep one day decided to make Go a major, if not the only, pastime in his life.

https://www.youtube.com/watch?v=ZvHL_lwfYYI

(His name is Morse - like the Morse code used in telegraphs.)

Fox 1d in 3 years is not bad but far from exceptional (it's not better than EGF 4k I think). I'd rather choose another method than solving 80k tsumegos.

Morse indeed!

It's not exceptional but it's a data point and we can use more data points, including the method used. In this case, arguably 80k tsumego did not provide for a fast track or steep curve. On the other hand, it's also interesting to understand what keeps people motivated, other than improving rank.