is people are not completely rational.
Prospect theory is an attempt to model behavior rather than to model what is 'rational' in economics.
The way I see it is there is no way in heck I am going to be disciplined enough to invest the 20$ per month. I am much more likely to invest it when I receive a large lump sum as opposed to an extra 20 I can just use on groceries.
It is interesting for sure.