A couple years ago I was changing the ATF and filter in my Nissan. After I got home with the new filter/gasket and a couple gallons of ATF, I pull into the garage, put the car up on jackstands, crawled under, drained the transmission, and dropped the pan. Carefully removed the bolts that hold the filter to the valve body and lowered that out of the way.
Spent an hour cleaning up the pan, removing the old gasket material, cleaning the magnet, etc. Hop back into the car, grab the new pan gasket out of the box, carefully lay it onto the pan flange, got it all lined up, hop back under the car where I carefully put the pan back on, and torqued all 20 or so bolts just right.
Went around front and under the hood, popped the dipstick out, and poured four quarts of ATF into the transmission.
Cleaned up all my tools, put them away, went inside, washed up, put on a new jacket, and went back into the garage.
Glad that this dirty, smelly job was behind me and I was good to go for another couple years, I cheerfully hop into the drivers seat, and started her up. I reach over to the shifter to row it through reverse, neutral, drive, etc before I confirm the ATF level on the dipstick, and with the engine running and foot on the brake pedal, as I look down toward the shifter, it catches my eye......
The Autozone bag, with the open filter box sitting on top of it... and my brand new filter sitting on top of the opened box, neatly wrapped in its clear bag, waiting for me to put it on. Not only did I forget the new filter, I forgot to put ANY filter back on. I shut the car off, sat there for a minute, gazing expressionless into space, uttered a few expletives, and started all over.
My two hour job turned into a four hour job.
That job out of the way finally, I figured I'd change the oil in the Sequoia while I was out there. Pulled her in, dropped the big metal skidplate, and drained the oil and removed the filter. New filter on, drain bolt torqued, and reinstalled the skid plate. Filled it with new oil, started it up, oil pressure good. A quick check underneath... no leaks.... good to go. I back out of the garage and take a short hop around the neighborhood. I pull back in the driveway and slowly approach the garage. I figured I'd just pull back in and check the dipstick and top up if necessary. I creep in and the truck comes to a sudden stop. Must be rolling over a stray socket or something, so I give it a tiny bit of gas. The truck strains a little and goes nowhere. I'm about 3/4 of the way in, so figuring I had room I give it a tiny bit more gas this time. Finally it lurches forward and as it does that... KA-BLUMP..I hear a slurpy thud. I throw it in park, mutter out a loud "what the censored did I just do??" and take a peak under the truck. There was my flattened drain pan, sitting under my right front tire, and seven quarts of used oil are quickly flowing toward my shoe, dripping off the tire, the underside of the truck, dripping down the garage wall, and drowning the tools on the garage floor.
Some days you just shouldnt be working on cars.