Originally Posted by Lord Chaos

Derailer gears are confusing at first. When I got my current mountain bike it came with the modern dual-lever shifter. I thought I'd never figure it out. One day, though, I was having problems with it staying in gear, so I had to start messing with adjustments. My first attempts made things worse, which meant I was adjusting the right thing in the wrong way. After some more tweaking I got the bike working better than it ever had; Performance I'd accepted as being "just how these things work" turned out to be due to basic misadjustment from the day I bought the bike.

So, I encourage experimentation. The more you know about this the better off you'll be when something breaks. I was riding with a friend one day when the cable to his rear derailer broke at the shifter. We still had a long steep hill to climb, and being stuck on the smallest sprocket would have made it unpleasant. We used his multitool and some cable ties to anchor the cable with the derailer on one of the bigger sprockets, and then used the barrel adjuster to make it run smoothly. He then had a three-speed with decent ratios.