Many Greeks work very hard. The top companies in Greece employ some very competent people (many have studied in the US, Germany or the UK and have worked abroad). The work ethic is intense and quite competitive. (I'm not Greek but have worked there for two years.) The very low minimum wage combined with high retail prices (Greece imports a lot) means that people have to work hard just to keep their heads above water.
Check the names in any British or US faculty (especially in science/medicine/IT) and see how many first or second generation Greek names there are (answer: lots, considering Greece is a poor Balkan country of 11 million inhabitants). These people have risen to the top in a very competitive environment through talent and hard work.
OTOH you see things in the public sector in Greece that make you shake your head and wonder/despair.
Without resorting to stereotypes there are some fundamental problems in Greek society. Politically and socially it is a deeply divided society. There is a general lack of trust in institutions (some of it justified) and plenty of corruption in some corners. Perhaps as a result of this many Greeks tend to be rugged individualists and look out for number one, which perpetuates things. Greece was colonized by the Ottomans for centuries (kiss of death for any country) and largely missed out on the industrial revolution of the 19th century. It suffered several catastrophic wars in the 20th century: the great Anatolian disaster in the 20s and WW2. The civil war (reds vs. whites) just after WW2 lasted 3 years and only ended in 1949. There was a military dictatorship in the 70s. These are all comparatively recent events. No wonder the country is messed up.