Yep, "Stupid is as Stupid does..." is a good topical quote for the human factor.

I've circumvented procedure for whatever reason more than once and been nailed for it too. It happens to the best of us I suppose. We all have our stupid moments; the lucky ones survive and hopefully learn an unpleasant but important lesson.

Now, as with firearms, I assume the item in question is in a potentially lethal configuration until I've proven that it isn't, such as using a probe, locking out the circuit, etc. I go through the checklist, and if I am not familiar with the circuit, then I don't proceed until I am. I don't rely on someone else to tell me it is okay anymore. I check it myself, and check my test equipment against a known standard so I know the test equipment is working as it should. You can never be too careful.

Even so, there are inherent risks in such endeavors that simply cannot be totally mitigated. There is no such thing as foolproof, or 100%, or totally isolated. But if you take the necessary steps to eliminate the most likely threats, and be wary of the murphy factor, then there is a certain amount of hazard that I guess we can live with, or else we'd never get anything done I suppose.

It took time and experience for me to become worth my salt as a technician, even with the best training up front money could buy. I don't make the sort of mistakes that created unnecessary hazards in the past, but I still make mistakes, and I still face hazards even now. I am not as sloppy nor as hasty about things as I was at first. Taking 500 volts across the chest will educate you pretty well I reckon, if you survive it, which I was fortunate enough to do.
The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)