We live by a combination of judgments that are based on our own informal observations and confirmations, "wisdom" that has been passed down from others, and scientific proof that we may learn about on or own or that may have been taught to us.
Scientific proof is given an elevated status when the reputation of the scientific community that is offering the proof is well established. We are highly unlikely to doubt that second hand smoke causes smoking related diseases. We are also unlikely to doubt the information that doctors and nurses give us when they tell us what our contributions to our own medical care should be.
Scientific proof carries much more weight from the reputation of scientists in conducting repetitive and controlled experiments that offer proof to an acceptable level of certainty. Every aspect of the process, from information gathering to actual quantitative and qualitative analysis and testing is rigorously examined and is expected to meet the highest standards of objectivity and factual proof. Scientists have both a body of knowledge and a discipline of thought that is not found in the average person.
The average person has both a body of knowledge and a more flexible discipline of thought that incorporates time tested and ancient wisdom and information from a variety of new sources, including informal and impeachable sources, such as word of mouth. Common sense also comes from formal sources, such as fact-checked journalism, books, and the counsel of scientists, such as doctors and teachers. Common sense is informally tested again and again in the real world, with far less control, objectivity, and proof . There is far less cognitive discipline, documentation, testing, and rigorous verification of facts. But, in the world of common sense, it is far easier to adapt to new information, whether it is good information or not, and to act on that information using whatever wisdom and knowledge is available, under times of stress, threat, or basic survival.
There are many, many situations where "scientific proof" is highly suspect. From rhetorical tools that are used to convince people, to infighting scientists who disagree about the validity of findings, modern lay persons are far more educated and skeptical than they were in the past. In the worst cases there are obvious charlatans who use the appearance of scientific advancement in order to sell products that range from dubious in the promises that are made, to dangerous in effect.
When a legitimate scientific discovery is established and confirmed, there are salespeople who want to sell products that are based on claims that the scientific discovery can be used to lose weight fast, cure wrinkles, or perform some miracle cure. The weight loss industry, alone, has used the discoveries about everything from hormonal activity, to the endocrine system and how it contributes to weight gain or weight loss. The profits are in the billions, but the success of such products is either minimal or not lasting.
So, ironically, most people use common sense as a tool for evaluating the claims made by both the scientific and the pseudo scientific communities. In evaluating the news stories that cover negative and even deadly side effects of new medicines, for example, a person will question the safety of a medicine when the doctor prescribes it. The person has no scientific proof that he or she will personally undergo the side effects, but will use common sense, or informally collected data, to question scientific authority, rather than to blindly accept it.
As a result, a combination of common sense, for making decisions that must be made without absolute proof, and a form of scientific discipline for critically evaluating information are essential these days.