Took me 6 hours to fix a $12 leaky faucet because I skipped the obvious step
Last Saturday I noticed a drip under the kitchen sink and figured it was a 20 minute job, so I grabbed my wrench and went at it. I tightened the packing nut, threw on some plumber's tape, and the drip kept coming back. Two trips to the hardware store off Route 9 later, I had a new cartridge and still no luck. Turns out the real problem was a hairline crack in the supply line, and the guy at the counter asked me one question that would have saved me the whole afternoon: did I check the line first? I never did. I just saw water and assumed it was the fixture. Six hours and $12 in parts later, the sink is dry, but my back hates me. What's the dumbest thing you skipped checking before you went and bought parts?