A challenge that most patent applicants face is whether their invention is obvious or non-obvious. If the former, the invention is not patentable.
The issue of obviousness is typically resolved by examining the prior art - such as patents and non-patent publications that preceded the filing of a patent application. If a person skilled in the art of the invention to be patented, and who is presumed to know of all of the prior art, would find the invention obvious, then the invention is not patentable.
However, common sense can also make an invention not patentable.
An example of common sense is in a Federal Circuit decision B/E Aerospace v. C&D Zodiac. The patent covered a space-saving technology for aircraft enclosures such as lavatories and closets.
A prior patent described a "first recess" in a wall to receive an inclined seat back of a passenger seat. The invention described not only a first recess, but also a "second recess" to receive a seat support of the passenger seat.
The patent Board found that it would have a matter of common sense to add the second recess to the first recess.
The Federal Circuit agreed with the Board and said that the "technology of the claimed invention is simple." The second recess "involves repetition" of the first recess, and that the "logic of using a recess to receive the seat back applies equally to using another recess to receive the aft extending seat support."
Simple inventions can be patentable. But if the simplicity is based on mere common sense, your invention may not be patentable.