Do you have a list of maintenance or diagnostic failures that just really took you for a loop?

I have several this year. The first one is diagnosing some electrical issues with my fancy Fluke 381 meter. Had totally conflicting readings within seconds a bunch of times and after a half hour I realized the test leads themselves had an intermittent short in them. At that point I thought back over the last several months thinking of my failures to figure out electrical issues on my planter and a pivot and it all came together. I can’t imagine how many days earlier my planting would have been done this year if it were not for those leads.

The other one is still too sore of a subject to discuss on here but I have been fighting it for 3 weeks and just got to where I understand the stupidity that has caused me so much of a struggle. Anyone else got anything like that?