Passage Summary: People usually only get worked up about health problems that are super obvious. Right now, everyone is worried about dirty water, so even though ozone is dangerous, they probably won't start a big movement for cleaner air.

Conclusion: It is improbable that a popular, large-scale movement for stricter air pollution regulations will emerge anytime soon.

Reasoning: Public concern is typically limited to the most obvious health threats; currently, people perceive contaminated water as a much more significant and widespread danger than ozone pollution.

Analysis: The statement in question serves as the foundational principle of the argument. It establishes a general rule about human behavior—that we only care about what's right in front of our noses—which the Professor then applies to the specific case of air pollution versus water safety. By showing that air pollution isn't the 'most obvious' problem, the Professor uses this principle to support the final prediction that no grassroots effort will happen. It's a premise that provides the 'why' behind the conclusion.