Carl Allen is at a standstill. No future... Until the day he enrolls into a personal development program based on a very simple idea: say yes to everything! Carl discovers with amazement the magical power of "Yes", and sees his professional and romantic life turned upside down overnight: an unexpected promotion and a new girlfriend. But he'll soon discover that better can be good's enemy, and that all opportunities shouldn't be taken.

The banker Carl Allen is a lonely man with low self-esteem after his divorce with Stephanie, for whom he still yearns. He avoids his best friend Peter. He has a boring job, stalled in a bureaucratic position in the loan department of a bank; and he spends his spare time watching DVDs. When he meets by chance his former high school mate Nick, he is convinced to participate of a self-help program called "Yes Man" leaded by the guru Terrence Bundley. The basic principle of the program is to say "yes" to new situations, leaving the negativism aside. Carl misunderstands the concept and says "yes" to every question. While leaving the encounter, he helps a homeless man and in the end of the night he meets the gorgeous Allison that helps him with her scooter. His life completely changes with his new attitude.