Coils can actually already be bad straight out of the package
Sometimes straight from the factory,
Getting a few months out of a coil is impressive, maybe its just your luck balancing out and you got a duff coil with a hot spot that burnt your cotton.
It might have even been solar flares reversing the gravitational pull. The point being getting sick burnt taste is not always going to be down to a vaper's control, nor is it always something anyone can diagnose.
I can get coils to last a while, as in a few months or so. Do I know how? No, at least not fully so. Yes, I build some of my own coils. Yes, I buy some already made up coils. I randomly alternate as to what coil I'm using on what deck. What that lets me come to know from experience? There's no real science, rhyme or reason to why or how a coil can turn otherwise yummy vaping jaunts into something tasting like flung monkey dung.
We can speculate and offer some advice, what's worked for us and maybe a thought why. Ultimately though we have to realize that sometimes
shit happens, all you can do is toss out a juice mix, toss out a coil build, start it over and hope for better. Sorry if that seems unfair or harsh. I don't recall vaping promising being
the panacea, no magic bullets exist no matter what they try saying about JFK.
I need to mix more Jesus-this-is-good/terrible-Junk juice although I'm kind of running my vg real thin.
*sniff, sniff*