486. Hindsight.

486.     Hindsight.

When assessing obviousness it is always necessary to guard against an ex post facto analysis because once the invention has been established, it may be easy to show how it might be arrived at by starting from something known and taking a series of apparently easy steps1. Where the prior art offers many possible starting points for further development it may not be obvious, without hindsight, to choose the one which leads to the alleged invention2.