From Tropic Thunder (2008):
Kirk Lazarus: Everybody knows you never go full retard.
Tugg Speedman: What do you mean?
Kirk Lazarus: Check it out. Dustin Hoffman, ‘Rain Man,’ look retarded, act retarded, not retarded. Counted toothpicks, cheated cards. Autistic, sho’. Not retarded. You know Tom Hanks, ‘Forrest Gump.’ Slow, yes. Retarded, maybe. Braces on his legs. But he charmed the pants off Nixon and won a ping-pong competition. That ain’t retarded. Peter Sellers, “Being There.” Infantile, yes. Retarded, no. You went full retard, man. Never go full retard. You don’t buy that? Ask Sean Penn, 2001, “I Am Sam.” Remember? Went full retard, went home empty handed…
This line from Tropic Thunder is often repeated as a joking admonition – there are “Never Go Full Retard” tee-shirts available on Amazon. The dialog above refers to Tugg Speedman’s career misstep in making the fictitious Simple Jack – a parody of Sean Penn’s I Am Sam – portrayed in Tropic Thunder as a commercial flop, panned by critics, and ignored by the Academy.
But was I Am Sam a career misstep for actor Sean Penn?
Sean Penn did indeed go home from the 2001 Oscar ceremony without the Best Actor Oscar. And the film received poor reviews from critics – the aggregator at Rotten Tomatoes has the film graded at 34% approval.
Otherwise, however, I Am Sam was successful.
First, the film was a commercial success. Box Office Mojo doesn’t list the film’s production budget, but similar films were made during that time for about $25 million dollars. I Am Sam grossed over $40 million in the United States. When foreign box office receipts are added in, I Am Sam grossed about $100 million – or something in the range of 4 times its production cost. 
Second, it is a little odd to suggest that getting nominated for – but not winning – the Best Actor Award for I Am Sam is somehow a mark against Penn and the film. There is no similar implication that Penn somehow suffered a career setback in getting nominated for playing Matthew Poncelet in Dead Man Walking, or a self-destructive jazz guitarist in The Sweet and Lowdown, and then going home empty-handed.
Sean Penn does as well as can be expected with Sam, but it is painful to see an actor of his fire and range locked into a narrow range of emotional and intellectual responses. Not long ago a veteran moviegoer told me that when he sees an actor playing a mentally retarded person, he is reminded of a performer playing “Lady of Spain” on an accordion: The fingers fly, but are the song or the instrument worthy of the effort?
3 Domestic: $40,311,852 + Foreign: $57,506,287 = Worldwide: $97,818,139. Box Office Mojo – I Am Sam (2001). Another similarity between Simple Jack and I Am Sam – they were both popular in Asia. I Am Sam made $36 million in Japan and South Korea.