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I mainly agree although I think that the trough of despair often comes after an initial bump. At first when designing the new system, you pluck the low hanging fruit of improvement for a small subset of the system. There is no dip yet -- things are just getting better. But when you start migrating the rest of the system, you inevitably do hit that dip and descend into the trough of despair before climbing back out.

The art is to design things in such a way so that a minimum amount of time is spent in the trough.