I work in software (web and database applications); sometimes I get feature requests on top of features request many of which are "urgent". In these cases (the bolded part of) this quote applies:
I went on to test the program in every way I could devise. I strained it to expose its weaknesses. I ran it for high-mass stars and low-mass stars, for stars born exceedingly hot and those born relatively cold. I ran it assuming the superfluid currents beneath the crust to be absent — not because I wanted to know the answer, but because I had developed an intuitive feel for the answer in this particular case. Finally I got a run in which the computer showed the pulsar’s temperature to be less than absolute zero. I had found an error. I chased down the error and fixed it. Now I had improved the program to the point where it would not run at all.
– George Greenstein, “Frozen Star: Of Pulsars, Black Holes and the Fate of Stars”