The feeling has been there for a very long time. Theodore Metochites in the 14th century lamented that the Ancients had said everything that needed to be said, so there was nothing left for his contemporaries to do. The Greek peasantry would make up stories about the pagan giants who built the inexplicable structures all around them.
The more superficial have translated the feeling of inferiority into the bombastic (“When we were building Parthenons, you guys were eating acorns”—noone that feels secure in themselves bothers to say that to Westerners). The more sensitive have had the feeling of failure gnaw at them. Dimitra Triantafyllidou’s answer does well to quite Seferis—who after all, as a professional diplomat, had plenty of opportunity to compare Greece to the West and reflect on what went wrong.
My sense is the feeling has dissipated somewhat as Greece became more integrated into Europe; there was a palpable difference I felt between my stay in 1983 and my return in 1995.