In 1948 the Palestinians were sure they couldn't fail, they outnumbered the Jews two to one and had the support of all the Arab states. In fact the Jews had nowhere to run and were so scared of failure that they gave the war everything they had. The sense that Israel's situation was precarious remained strong after 1948 and in the run-up to the 1967 war, Nasser's doom laden pronouncements led to widespread fear in Israel. Again it turned out to be the opposite: Arab overconfidence fed the Israeli dread of defeat and led to opposite results.
In 1973 the situation reversed: The Israelis thought they were undefeatable and the Arabs were sure they couldn't win. Although the Israelis didn't lose the war, it was the closest Israel has come to defeat.
Because many Arabs assumed victory was inevitable sooner or later, they didn't work for that victory and were at a disadvantage. Because so many Israelis thought the Arabs might be right, they were motivated to try harder. Thus inevitable victory fed defeat.
Six months ago Assad's defeat looked invitable, but right now its hard to say what will happen in Syria. Latest reports say 50% of the opposition to Assad are "global Jihad' volunteers. With so many Jihadi forces gathering, Assad may find friends in new places, expeically if he dumps his Sarin collection.
Things may be reversing again. The Arab states are a mess, but given the way things tend to fall upside down in the Middle East, I would hestiate to make any predictions.