Spark plugs. Why is it so hard?

I use the NGK as much i can. Had everytime good experience and no fouling except there was something not correct, f.e. during a engine diagnosis on customer cars. I never use a plug that falls to the floor, replace it. Tuned 2 strokes, classic cars, Wankel, nothing bad.
NGK has a good product finder tool. The NGK has a wider heat range than old Bosch plugs, so they forgive more.
Study also the explanations what the numbers and letters tells you about the plugs.