Answer:
It follows the "keeping the wording short and to the point" guideline.
Explanation:
It is known -even scientifically proved- that litmus papers are useful to measure basic, acid or neutral conditions of matter such as water. In order to avoid all the explanation, the ad uses the phrase "You Probably Know This: The Darker, The Harsher" in order to directly demonstrate that the darker the color of the litmus paper turns, the harsher condition the matter has.
