The reason why every sport stresses fundamentals are because they are very important to you work on them to the point it's automatic with your body due to muscle memory so at the top level wins and loses literally come to the little things
Great example 2009 finals when Courtney Lee had a chance to win the game but missed the lay up as the clock was going down
You get so good that you can be like Ray Allen to step back a step and hit one of the most important shots in NBA history
To me I understand not ever great can win a championship but there's something special about a great player repeating as champion the first year is hard the second year is harder because every team giving their best shot every night, teams and players changed to throw something new at you, you got the media throwing shots at you , you got coaches who were on your team the season before on a new team that know your tendencies, you got new teammates and rookies, you got teammates who didn't put work in over the summer or got fat , you got other teammates who got paid so they ain't got the hunger, injuries that take longer to heal while making you slower, and then you got yourself either aware of it from the start or aware of it as the season going on
A lot of it comes down to little things