It won't be the missed opportunities in Oklahoma City or the disappointment of the Big 3 Nets era ... no, according to Gilbert Arenas, if Kevin Durant can't win a championship in Phoenix, that would be the "biggest failure" of his career.
The former NBA star made the proclamation on Fubo Sports' "No Chill with Gilbert Arenas" this week ... after he said there's just no way in hell the Suns can lose the 2023 title.
He explained ... with Durant, Devin Booker, Deandre Ayton AND Chris Paul -- he promised the team would take home the Larry O'Brien Trophy later this year.
"Like," he said, "I don't know why we playing."
But, if they do somehow lose after acquiring Durant at the deadline earlier this month ... he said it will be a massive blemish on the future Hall of Famer's career.
As you know, Durant has had some forgettable moments in his 15 NBA seasons -- the recent destruction of his Nets squad as well as blowing a 3-1 lead to the Warriors in the 2016 playoffs come to mind. Arenas, though, made it known, losing this year would top them all.
But, the 41-year-old clearly believes it won't happen, saying on the show "this is not even a question."
"Chip," he added. "Chip with the dip."