In 1966, the DC circuit court wrote about how "serendipity is consistent with patentability" and how patent law leaves room to reward luck. California Research Corp. v. Ladd, 356 F.2d 813 (1966).
In some ways, serendipitous inventions are easier to defend as patentable because defendants are less able to point to "ordinary research steps" as the cause of the invention. This may be especially true post-KSR. Dissenting in Pharmastem, Judge Newman argued that this love of luck had gone too far – arguing the majority's denial of patentability was akin to "limiting the patent system to the serendipitous and the unexpected." Pharmastem Therapeutics, Inc. v. Viacell, Inc., 491 F.3d 1342 (2007).