The essay you link to is absolutely fabulous and I couldn't agree with it's conclusions more, but I know that I want to be a programmer. I 'always' (since 10) knew it and now, nearly twenty years later, which were filled with programming and little other than programming I'm still the same. I want to be a programmer, I struggle for mastery in nearly every aspect of my art/craft/... and I don't mind spending another twenty years in ever more obscure corners of it.
Now, this doesn't have to be the case for OP. Maybe he want's to create something which he can sell, or maybe he just wants to be literate in computers. There could be lots of reasons one wants to learn programming in 21 days (or 8 weekend, or whatever).
What I want to say is that although programming could eat your whole life in one bite not everyone wants this to happen and such people are perfectly right to try and learn a bit and then stop.
...sorry, I had a hard day at job today, I just needed to write something. Don't mind me :)
I think I've read this at some point -- I've at least seen the 10 years / 10.000 hours numbers before.
I did a quick calculation with respects to martial arts practice -- and if you want to get in 10.000 hours in 10 years -- you do indeed need to practice quite a lot.
Start with a strong foundation: 2 hours 3 times a week, 48/weeks a year. Add 5 hours of training every other Saturday (or Sunday). Take seminars. Lets assume they amount to a full week of training/year (40 hours). You'd still by below 500 hours/year -- and you'd take 22 years to attain "master" level.
This actually fits quite well with the arts that still do rigorous gradings, like traditional ITF Taewkon-do, or karate and koryu styles that generally have two sets of gradings, first grading up to 4th dan, then to instructor grades -- and 5-6th dan generally being considered "full proficiency".
It also follows a somewhat simple rule of thumb from the traditional grading systems (before splitting the white belt into many colours -- at which point it is no longer white, to paraphrase Gandalf): After 1 year of (intensive) practice grade up to 1st dan, practice two years for 2nd dan, 3 for 3rd and so on -- for 21 years to 6th dan (assuming no breaks or injuries).
I guess all this is neither here nor there, but I found the correlation interesting.
[1] http://norvig.com/21-days.html