What doesn't kill you makes you stronger has a lot of truth to it. If it's not a lethal dose it will only make them become stronger.
Resistance is what we saw in the honeybee mite treatments. There is a product called Apistan and later when resistance became clear, Checkmite, now neither is working on mites.
What happened is that the Apistan strips were killing 98% of the mites. The 2% that had some contact but did not die had offspring that were also resistant and all of their offspring was resistant thereafter. There was also some other issues of misuse like leaving the strips in after the treatment period and newly hatched mites were getting a diluted dose from the nearly depleted strip and not dying also contributing to the resistance.
People need to be educated about resistance or we will run out of tools to fight parasites. Much like antibiotics in humans and animals.