Tripp (Matthew McConaughey), a 35-year-old man, is still living with his parents Al (Terry Bradshaw) and Sue (Kathy Bates), in New Orleans. Tripp's best friends Demo (Bradley Cooper) and Ace (Justin Bartha) are also still living in their parents' homes and seem proud of it. Al and Sue are fascinated when their friends, whose adult son recently moved away from home, reveal that they hired an expert to arrange the matter.
The expert is Paula (Sarah Jessica Parker), who believes that men continue to live at home because they have low self-esteem. Her approach is to establish a relationship with the man to build his confidence and transfer his attachment from his parents to her. However, upon meeting Tripp, she finds that he does not fit any of her previous profiles, having normal social skills and no problems with self-esteem. After an awkward encounter with his parents, Paula thwarts his attempt to dump her and has sex with him, all the while developing real feelings for him. She and Tripp find themselves sailing unfamiliar waters and confide in their friends.
Paula's vocation exasperates her roommate Kit (Zooey Deschanel), who believes that Paula took the job because she once had her heart broken by a man who lived with his parents. Paula, on the other hand, is shocked when she finds out why Tripp lives at home: his life collapsed when his fiancÃ©e suddenly died, and his family has been his source of solace ever since.
Ace discovers what is going on and blackmails Paula for a date with Kit; although Kit is more attracted to Demo, she and Ace wind up falling in love. Ace then outs Paula to Demo, who in turn reveals all to Tripp. Tripp angrily confronts his parents, and breaks up with Paula. Wracked with guilt, Paula refunds Al and Sue's money. After an awkward confrontation, Tripp manages to forgive his parents, but he cannot forgive Paula for manipulating him.
Tripp's parents and friends devise a plan to reconcile the two lovers. They tie up and gag Tripp and lock him and Paula together in a room. Paula pours her heart out to him, and he finally forgives her. The film ends with Al and Sue in their empty nest, happily singing "Hit the Road, Tripp", fading into the closing credits playing the actual Ray Charles song, and Tripp sailing away with Paula on his newly purchased boat.
Why do men continue to live at home according to Paula?
Because they have low self-esteem