[t43562]

Big upfront designs are obviously based on big upfront knowledge which nobody has.

When they turn out to be based on false assumptions of simplicity the fallout is that the whole thing can't go forward because of one of the details.

Evolutionary systems at least always work to some degree even if you can look after the fact and decide that there's a lot of redundancy. Ideally you would then refactor the most troublesome pieces.

[bluGill]

Big upfront design always tries to design too many things that should be implementation details. Meanwhile the things that are really important are often ignored - because you don't even realize they are important at the time.