williams was suspended from nbc in february after it emerged he 'd lied about being in a helicopter that was shot down in iraq in 2003 .
a new report in vanity fair claims williams lied because he felt insecure taking over from beloved anchor tom brokaw at the nightly news .
while some execs saw his lying as ` quirks ' of his personality , the tales left brokaw ` incensed ' and he ultimately did n't support williams in february .
after he was accused of lying , williams wondered if he had a brain tumor .
but other nbc employees said williams had always been out of his depth because of his lack of experience and disinterest in ` hard ' news .