'I'd like to thank all the people who will still employ me...'

You win an Oscar, your career is set, yes? Not necessarily – it's what you do next that counts, says Geoffrey Macnab

So what do you do next? This is the question that regularly vexes Oscar winners. On the night they win their statuettes, it seems that they have been given the keys to the magic kingdom but all too many promptly manage to get lost. Whether through erratic advice from their agents and managers, their own wilful stupidity, or sheer bad luck, they fritter away the goodwill and most of the career opportunities.

It was very curious indeed to see double Oscar-winner Hilary Swank (Boys Don't Cry, Million Dollar Baby) attending the birthday party last autumn of Ramzan Kadyrov, the president of Chechnya. Although she subsequently apologised and was reported to have sacked her manager, her (paid for) appearance at a party hosted by a dictator described by the soon-to-be-murdered Russian journalist Anna Politkovskaya as "the Stalin of our days" was a career blunder on a monumental scale. Thankfully, Jean Dujardin (who won his first Oscar last week) hasn't been consorting with Eastern European tyrants. However, the French actor who gave such a dashing performance as the Douglas Fairbanks-like silent movie star is already embroiled in controversy, less than a week after making his Academy Award acceptance speech.

The problem is that Dujardin has gone back to his Gallic roots. He is one of the directors and stars of new French portmanteau pic Les infidèles (The Players), a raucous comedy drama about French "male infidelity in all its desperate, absurd and wildly funny variety" (as the producers describe it.) In the section directed by The Artist's Michel Hazanavicius, Dujardin plays a businessman determined to commit adultery before going home from a company conference.

Judging by the critics' sniffy responses ("Uggie the dog almost certainly conducts his sex life with more discretion than the dopes on display here," complained Screen International), this is one film that certainly won't be winning any Oscars.

Worse, Dujardin's image appears on the poster. It doesn't show the actor at his most dignified. He is pictured in a bedraggled business suit, holding a pair of naked female legs and saying "I am going into a meeting". It's more Benny Hill than French art-house cinema. Predictably, although the film is satirising leering middle-aged French men struggling to control their libido, it has been accused of rampant sexism. If Dujardin was angling for future roles in Disney films, this wasn't an astute way to go about it.

In the Darwinian world of Hollywood, it's astounding how quickly even the most firmly established stars can lose their footing. That is one of the main themes of The Artist. Audiences want "fresh meat". If there is just a whiff of decay about an actor or film-maker, they will quickly be discarded.

There are many stories about Oscar winners who've fallen from grace. When Halle Berry became the first woman of African-American descent to win a Best Actress Academy Award for Monster's Ball, it was a fair assumption that she would become a major figure in Hollywood. However, roles in Die Another Day and Catwoman didn't enhance her credibility. She has been given the opportunity to make very few films since that have stretched her as an actress.

A further cautionary tale is that of the young Dutch director Mike van Diem, who won a Foreign Language Oscar in 1998 for his costume drama, Character. Van Diem, who had also won a "student" Oscar a few years before, was signed up to direct Spy Game (2001), a huge Hollywood film starring Robert Redford and Brad Pitt. However, van Diem left the project before shooting, citing concerns about its "scale and tone." Almost 15 years after his Academy Award success, he is yet to direct another feature.

Van Diem's compatriot Marleen Gorris is yet another Oscar-winning film-maker whose career hasn't flourished in the way that might have been anticipated. When Gorris won her Oscar (again for Foreign Language Film) for Antonia's Line in 1995, she looked set to emerge as a major European director. She helmed a moderately well-received Virginia Woolf adaptation, Mrs Dalloway (1997), The Luzhin Defence (2000), and Carolina (2003), a romantic comedy starring Shirley MacLaine. Nonetheless, her career tailed off. Although she did go on to make Within the Whirlwind (2009), her experiences underline the dilemma that often faces European Oscar-winners. They have the chance to work on a broader canvas and with major stars, but with this opportunity comes a loss of freedom. At the same time, they risk becoming uprooted from their own film-making cultures.

London-based Luise Rainer, now 102 years old, out-Streeped Meryl Streep in her day. Not only did she won two Best Actress Oscars, she won them in consecutive years, for The Great Ziegfeld (1936) and The Good Earth (1937.) She was up against ferocious competition from the likes of Greta Garbo, Norma Shearer, Carole Lombard, Barbara Stanwyck and Janet Gaynor. However, unlike Streep, she wasn't able to continue racking up the Oscar nominations. Her career rapidly went into a tailspin.

"Rainer became the most extreme case of an 'Oscar victim in Hollywood' mythology," critic Emmanuel Levy wrote of her. "Her dwindling career prompted gossip columnist Louella Parsons to coin the phrase, 'the Oscar as a jinx'." The challenges that winning Oscars can pose are self-evident. Recipients often begin to take themselves too seriously and thereby risk growing away from their audience. They try too hard to emulate a success which may have been accidental.

Colin Welland famously declared "the British are coming" when he won a Best Screenplay Award for Chariots of Fire. Of course, they weren't really. Nor did director/comedian Roberto Benigni's seat-climbing antics when he won an Oscar for Life is Beautiful lead to any great flowering in Italian cinema. With the exception of hardy perennials like Streep, Martin Scorsese, Woody Allen and one or two others, Oscar success for most film-makers and actors is strictly on a one-off basis. That applies to Americans as much as Europeans. There are many US actors, from Timothy Hutton in Ordinary People to Mira Sorvino in Mighty Aphrodite, who've failed to trump their Oscar successes.

Still, even if an Oscar doesn't open up the brave new world of opportunity that its recipient may have imagined, we're not quite talking poisoned chalices here. Ask any of the award winners if they'd like to give their statuette back and it's a fair prediction that the response will be a very resolute "no". Whatever the subsequent hangover, the euphoria and sense of making history will have been compensation enough. Who cares what happens next?