A patent will not be granted if it’s obvious. But what if it’s only obvious after the fact?
The paper clip was patented. The toilet-paper holder was patented. The “one-click purchase interface” for Amazon’s online sales was patented. They all seem pretty obvious to me now, years later when I realised just how valuable each patent later became, not during the patent application process.
Inventiveness is determined at the date the patent is filed (its priority date). The case law has grown up around not allowing experts in a case to take the role of an “armchair critic” by saying that in hindsight, the invention was obvious.
To test obviousness from a later date would be unfair to an inventor. Unfortunately, experts still sometimes convince courts and examiners are guilty of alleging that the invention was obvious at the time of filing when all they are doing is looking back with hindsight. No one can say this does not happen, but hopefully, it happens less rather than more.