What are the rate-limiting steps in drug discovery?

There are terms used in chemistry that could help the lay public out quite a bit, if only they knew them. One that I’ve seen many non-chemists applaud is the concept of a ‘rate-limiting step’. We chemists are used to thinking of reaction mechanisms with several discrete stages, and realising that they don’t all run with equal facility. One particular part of the process (a bond rotation, a rearrangement, an anion formation or whatever) will turn out to be the bottleneck for the whole thing. Nothing you do will speed up the overall reaction unless it addresses that particular slowdown.