O'Neill had once been heavily touted in the media for a big job like Liverpool or even Manchester United but now the 61-year-old's reputation is at an all-time low with 16th-placed Sunderland having slipped to a point above the drop zone.
Nevertheless he is adamant he deserved the chance to try to save the club like last season, when he took over in December 2011 and won seven of his first 10 games.
"Coming into the football club at the time when the club was on its knees, and I believe I saved the club from relegation last year, I felt the opportunity [to stay] should have still been afforded to me," the former Celtic and Aston Villa boss told the BBC.
Italian Paolo Di Canio, who has had to fight off accusations he is a fascist, succeeded O'Neill on Sunday and has seven matches left this term to try to guide the north east club away from trouble.
His first game in charge is Sunday's trip to Chelsea, with O'Neill's last match at the helm a 1-0 defeat at home to soon-to-be-champions Manchester United.
Pundits questioned the reasons for sacking the Northern Irishman after a game he was not expected to win but nothing surprises O'Neill, who quit Villa just before the start of the season in 2010 over what he saw as a lack of investment.
"I'm still disappointed and frustrated but life goes on," he said of his sacking by boyhood club Sunderland.
"I'm in the business now where I think very little shocks you about professional football, particularly in the last 10 years. I think you can nearly lose your job in management if your tie doesn't fit your suit."
While O'Neill feels he did not deserve the sack at Sunderland, Southampton goalkeeper Kelvin Davis has revealed he thinks the unpopular dismissal of Nigel Adkins in January was the right move.
The south-coast club, who admirably drew 2-2 at Chelsea just before Adkins' departure, have since climbed the Premier League table under Argentine Mauricio Pochettino.
"The manner in which he has come in and lifted the club to a new level shows it was a decision that's been proved right," Davis said.
Adkins is now at bottom side Reading, who host 12th-placed Southampton this Saturday.
