... in that he lost everything he ever had by age 40, although Kane didn't die broke by any means. An athlete expects to lose their prowess over time, but Jake lost everything else too. He did have a pretty good second act, partially and ironically because of this film, and even managed to live to age 95 and not die alone. That's an unexpected outcome when you first see him at age 42.
It's really interesting how this film is set up. You first see LaMotta (Robert De Niro) at age 42 in 1964 - bloated, working in a dive of a nightclub, practicing the third-rate act that keeps him fed and off the streets. His name and the year are shown in print. Then immediately you switch to LaMotta in 1941, in the ring, at age 19. Granted, Robert De Niro at age 36 when he made this does NOT look anything close to a teenager, but then there has to be some dramatic license.
This first fight shown in 1941 tells you what you need to know about the kind of world Jake inhabits. There are the violent punches of the fight followed by a decision against Jake with which the audience strongly disagrees. Fans throw things - everything from popcorn to chairs. Fights break out. A woman is trampled in the chaos. And then the organist tries to calm things down by playing the Star Spangled Banner. The audience does not come to attention.
So you've seen the end and the beginning of the story. It's fascinating and grabs one's attention, and even though you can look up and see how the actual Jake LaMotta's life went in those 23 years, the movie gives you all of the intimate scenes telling you the how. Jake craves love, food, recognition - he has a tremendous appetite for all of these things but he's also tremendously lacking in confidence and self control and strikes out violently as a result. It really is a fascinating portrait.
