THE ANSWER
Plucking pulls hard on the follicle, and the follicle often does not return to its original shape. A distorted follicle is harder to treat permanently later, needing more sessions, and regrowth from repeatedly plucked follicles tends to come back coarser. Tweezing does not create new hair, but it does make the hair you have harder to get rid of.
Why
Pulling a hair out means overcoming the grip of the follicle around it. That force is applied to the follicle wall, and repeated over years it can leave the follicle curved or bent rather than running straight from surface to root.
This matters specifically for permanent removal. Electrolysis works by following the hair down its own follicle with a probe. A straight follicle is straightforward to follow. A distorted one is not, and a probe that cannot reach the growth cells cannot finish the job in one treatment. So the same hair needs treating more times, and the area takes longer overall.
The coarser regrowth people describe is a related but separate effect. Repeatedly disturbing a follicle can prompt it to produce a heavier hair, and people commonly report that a hair plucked for years is thicker than it was.
Worth separating from shaving, which does none of this. Shaving cuts at the surface and never touches the follicle, which is why it is the right way to manage hair between electrolysis sessions.
Does tweezing make hair grow back coarser?
People consistently report that it does, and repeated disturbance of the follicle is the usual explanation. What is not in question is the distortion effect, which is described consistently across electrology sources.
Is it bad to keep plucking chin hairs?
It is the most understandable response to one or two hairs and it does make later permanent treatment slower. If you intend to treat the area permanently at some point, stopping sooner costs you less.
How long before my appointment should I stop tweezing?
Generally several weeks, so hair is present in the follicle to be treated. Most practitioners will give you a specific timeframe, and it is worth asking rather than guessing. See how to prepare for electrolysis.
What is a distorted hair follicle?
A follicle that has been pulled out of its natural straight shape, usually by repeated plucking or waxing, so it curves or bends. It still grows hair. It is simply harder to treat.
What the evidence says
Follicle distortion from repeated plucking and waxing is described consistently across independent electrology sources, and it is a recognised reason treatment takes longer in areas that have been plucked for years. The related claim that regrowth becomes coarser is widely reported by practitioners.
What to do next
Stop plucking the area now, whether or not you have an appointment booked. Shave or trim instead. Shaving does not make hair worse, which is covered on does shaving make hair grow back thicker.
If you have plucked an area for years, it is still treatable. It simply takes more patience. See chin hair removal or upper lip hair removal.