In Gillette Co. v. S.C. Johnson & Son, Inc., 919 F.2d 720, 16 U.S.P.Q.2d 1923 (Fed. Cir. 1990), the Federal Circuit affirmed the district court’s determination that U.S. Patent No. 3,541,581 on a shaving preparation was not invalid under 35 USC 103.

The Federal Circuit rejected Gillette’s obviousness argument as based upon hindsight, quoting from Milton’s Paradise Lost:

The invention all admired, and each how he
To be the inventor missed; so easy it seemed,
Once found, which yet unfound most would have thought,
Impossible!

PARADISE LOST, Part VI, L. 478-501