> Rarely have I seen a class that truly needs 20 parameters

If a class seems like it needs that many parameters, it is very common that one or both of these is true:

1. It is doing too much, or

2. There are things-that-should-be-their-own-classes hiding in groups of the parameters.

#2 is kind of a subset of #1, but the "doing too much" tends to be concentrated in validating relations between parameters rather than what happens after the object is constructed.