Passage: After filming Where the Heart Is, Portman moved into the dorms of Harvard University to pursue her bachelor's degree in psychology. She said in a 1999 interview that, with the exception of the Star Wars prequels, she would not act for the next four years in order to concentrate on studying. During the summer break from June to September 2000, Portman filmed Star Wars: Episode II – Attack of the Clones in Sydney, along with additional production in London. In July 2001, Portman opened in New York City's Public Theater production of Chekhov's The Seagull, directed by Mike Nichols; she played the role of Nina alongside Meryl Streep, Kevin Kline, and Philip Seymour Hoffman. The play opened at the Delacorte Theater in Central Park. That same year, she was one of many celebrities who made cameo appearances in the 2001 comedy Zoolander. Portman was cast in a small role in the 2003 drama film Cold Mountain.

Question: Why did Natalie Portman decide not to act for four years?
to concentrate on studying