He was a legimitate underdog in 2007, 2014, 2015, 2016.
In '07 he went up against a highly pedigreed dynasty at 22 years old with the worst supporting cast of All-Time. No chance any superstar player ever wins in this predicament.
In '14, the Spurs were favorites this is the best Spurs team they've had. The Heat defense fell off a cliff and Wade was looking flabby. Also, the media pushed a Spurs revenge narrative, and pushing for a fifth Tim Duncan ring, and looked to push Kawhi as a superstar in the making.
'15 pretty self explanatory. LeBron vs. a 67 win Warriors team with no Kyrie or Love.
'16 again pretty self-explanatory. Facing the G.O.A.T. regular season team.
LeBron's faced some tough ass teams in the Finals.