if im walking something went drastically wrong. Like I broke a chain or a derailleur exploded and I couldn't get it back together. It's common to see noobs and or racers walking home because they were too cool to carry a pump or didn't know how to use their c02. I'll usually offer to help them as ill have a pump of some sort, a tube and a well stocked patch kit. If I'm feeling really lazy I'll just put in a new tube and patch the flat tube later, but the time different in patching vs changing a tube isn't so much that it matter so much.btw the key to doing a good patch is letting the glue dry before you apply the patch.