Another really important consideration is the Stripper and Crimper. I use Klein Tools.
Unfortunately with out sourced mfg. the wire may not be what it's described as being. The actual diameter of half a dozen different brands of '12 gauge stranded copper' may vary considerably. Just picking the '12 ga' slot on a stripper is no guarantee that it's correct for the wire. Aslo there's two different types of strippers, one for Solid wire and one for Stranded wire! They're nowhere near the same outer diameter in the same gauge number! A practice run is needed to identify exact diameter, relative to the strippers in addition to knowing what tool you have.
A close look at freshly stripped wire may reveal a very slight cut in all or some of the outside conducters, setting it up for premature failure. I'd rather work harder to use a larger stripper jaw and 'pull' insulation than get a quick strip that nicks the strands.
Also important that the crimper fits the particular terminal as closely as possible. Some will over-crimp, damaging the conductors but its invisible inside crimped terminal. About the same as nicking them, they're crushed or scarred or whatever which again starts the work hardening, along with a weakened area of concentration right next to or inside opening of terminal.
Proper tool for the job always applies whenever possible. I knew a guy out in the field that could strip wire and crimp terminals faster and better with a Klein Electricians Knife and standard crimper than anybody else could do with an automatic stripper! He got top bucks and was specially imported on the big jobs thanks to 35 years experience.
Technigue is often lacking in electrical wiring simply because most guys rarely do it and haven't really studied the principals at work.