It is basically a challenge against gear acquisition syndrome. Challenging yourself on using just one camera body and one lens. Preferably a fixed focal length prime lens.
I'm using a humble Nikon D90 for all my photography work and I have a typical 3 lens kit with 18-55 + 55-200 and a nifty fifty. The Nikkor 50mm F/1.8D is the best among this little tree lenses. I used to own a Sigma 70-300 APO DG, a Nikkor 55-300VR G and a 18-105VR G. The nifty fifty is the sharpest and fastest one among them and gives the best results in almost every condition. One day I realized its the lens I mostly use for almost everything. So why bother carrying a heavy back pack for other lenses?... I had a small shoulder strap bag that can carry my camera body with lens attached to it, my Metz flash, Raynox Macro Extension, memory cards, battery pack etc. I put all these to that one small bag and every time I go out I grabbed it with me.
I had a tendency to use what it best anyway. The best results I could get was with my Nikkor 50mm F/1.8D lens on my Nikon D90. This is a humble kit... For many people out there this is out of question because they believe the better the equipment the better your photos get. Equipment helps a lot of things but you can not buy the talent - you can only improve it.
Many photographers out there have huge diaries and chronicles about their one camera and one lens experience but it wasn't that much of a big deal for me because I'm already doing it.