What do I think?
Greeks have historically been smart people, but there is no way to tell if today they are smarter than the people of other countries. The real problem is that about 90% of Greeks believe they are much smarter than the rest of the Greeks (and the rest of the world).
Believing that you are smarter has no value unless you can prove it, by doing something smarter than average. And the easiest way is to outsmart someone else or even better outsmart the "system"!
I will define "systemically unstable behavior" as something that if the majority performs within a system then the whole system gets screwed, including the actor. Trying to outsmart others or the system is systemically unstable behavior with regards to society.
In a nutshell, that's what happened to Greece. The 90% did 'smart' things and thought they would get away with it, that others would pay the so called negative externalities.
So many times I had heard the answer "But Everybody Does it, I would be stupid if I don't do it too" as an excuse for something inappropriate somebody did. This thinking is built into the Greek DNA.
Can this mentality change?
I don't think so, it might be temporarily put aside, but it is really the curse of the modern Greeks.