And the corrolary to that, is, "I'm fixing this one thing" but you find several other things that need fixing too....
I had an oil change and a belt tensioner, turn into a water pump, timing job, including new cover, oil pan removal and gasket, hoses, and prolly a couple other things I forgot. Shoulda been an afternoon's job and it went three weeks.
Also did complete tie rods and sleeves on our '90 Burb in an afternoon, and spent over a week getting lower ball joints in it cause they kept fighting coming out.
And had brake work get delayed because I found out the upper ball joints on another Burb, were completely worn out. Bolt in units, but weren't too interested in coming out of the spindles....yes the new ones got anti seize on the shafts.
And in both cases I was using the appropriate pullers. Got to use a BFH a bit too....