In my time as a research assistant at a drug discovery & development laboratory, I ran into a particular issue that I believe had the potential to affect the critical path of the project I was working on. The drug I was charged with synthesizing had two parts: a ‘backbone’ (which was a standard base molecule that different substituent groups were added onto) and the specific substituent group. After each synthesis step in the building of the target molecule, there were purification procedures that were thought to be trivial. However, after on particular synthesis reaction, the byproducts and the target drug compound were so similar in weight and polarization that separating them became a real challenge. Very quickly, this previously thought trivial step turned into a few day ordeal; quickly putting it on the critical path. Lucky, there was enough slack time built into the method to account for such an issue to not affect the targeted final drug testing date.