Wikipedia has a cool chart that shows what kind of state you're in for various levels of challenges and skills. If you perceive the challenge level to be high, and your skill level is high too, then you're in a state of Flow. This is the state any programmer, athlete or any other practicioner will want to achieve. It's the feeling that you couldn't do any better than you are doing right now, and it's taking all you have to accomplish it. I have to admit that I have lost this feeling of Flow at work when programming. The challenge is gone, and depending on the day of the week I am either in Control, Relaxation or Boredom. Cycling however is a completely different matter.
I remember two years ago I used to have trouble keeping a steady pace in the third-highest gear of my bicycle, but it was just enough of a challenge to enjoy cycling. These days, despite my having gained weight (again >_<;) I now feel more comfortable in the second-highest gear. That's how I can still enjoy cycling; if things get too easy, just shift up another gear.
On a practical note: I did make things a bit too difficult for myself tonight. At first I didn't pay enough attention and almost hit a truck while turning onto the main road. Well, more accurately described, the truck nearly hit me. I doubt the truck would notice -__-. Anyway, being throughly demotivated after that stunt, I did finally decide to continue cycling to the seaside in the wonderful foggy and damp weather we are experiencing for the past couple of days, only to find myself extraordinarily exhausted when I arrived. I had had a similar feeling before, which was when the rear brakes were kind of broken and were touching the rear wheel while on the move, creating a very large amount of friction. That problem had been fixed for a long time though. Or so I thought. As it turns out another problem caused the brake problem to re-appear. The rear wheel is wobbling heavily from left to right, and it had been getting worse the past few weeks. I guess it finally became bad enough for the wheel to hit the brakes again. After disabling the rear brakes everything went super smoothly all of a sudden, and I experienced a new sustained top speed on the way back :D (although I have no proof because the damn GPS broke right after the Africa trip...) Final time: 34m26s.
Note to self: my bicycle sucks!