In the 1975 Stanley Kubrick film Barry Lyndon, the main character Redmond Barry ascends the social ladder to transform himself from a countryside farmer to a member of the aristocracy. During his search for a title to secure Lady Lyndon's wealth, in case she passes away, Redmond begins to experience a series of unfortunate events that ultimately result in him falling back to his original place in society - yet much older in age and lesser in strength. What actions had caused his own downfall?
Pride is probably the major one. Also lack of character that is expressed in his vices and petty cruelty. Cruelty, especially to the little Lord Bullingdon in the form of physical abuse, and to Bullingdon's mother though open infidelity, is what really takes him down in the end. When Bullingdon, a great lord, eventually comes into his inheritance, he forces the now powerless Barry into banishment.
The cruelty to Bullingdon is also what causes Barry to be "banished" from the polite society of the high aristocracy, per the scene at Lady Lyndon's birthday party. Bullingdon uses the party to publicly call Barry out, which leads Barry to publicly beat Bullingdon. This specific act makes Barry a social pariah.
Mercy, at the wrong moment, is also a factor. Barry's decision not to shoot Bullingdon in the duel, even though he has the upper hand, leads to Barry being shot in the leg by Bullingdon. When Barry is convalescing from the injury, Bullingdon seizes control of his estate.
Act II Plot summary from Wikipedia has all the details.