imagine you spray this once, and then spray it 9 more times. 100% germs. wait no because the germs will get rid of the 10% and there's- WAIT it can't kill those specific germs, so then spray it 9 more times, and the theory still works!
If there are a million germs in a jar and spray cleaning spray on it that promises that it will kill 99.99% of germs then 100 germs are still in the jar