Work at a shop for a week and you'll see some stuff...

Girl came in for a helmet the other day and some air in her tires. She had ridden there at about 18 psi, chain the color of a beautiful sunset, when I grabbed her bike I thought the front hub was really loose until I realized the 17mm hardware store nuts on the axle weren't even finger tight, etc... Not sure how she rode the couple miles to the shop without dying, and here's the kicker: after applying lube to the chain, airing the tires, and securing the axle I bet she didn't even notice an improvement.