The idiom "a bridge too far" means a target that is too ambitious, particularly one that will end up causing problems or even dire consquences. A similar cliché is "biting off more than you can chew." The idiom "a bridge too far" is based on Cornelius Ryan's 1974 book A Bridge too Far, which was made into a film of the same name in 1977.

The non-fiction book A Bridge too Far tells the story of Operation Market Garden during World War II in September 1944. In this operation, the Allies attempted to get past German lines and seize several bridges in occupied Netherlands. The idiom and the title of the book come from a quote by British Lieutenant General Frederick Browning, who said “I think we may be going a bridge too far” before the operation started.

The Allied forces were able to seize several bridges but were delayed by the demolition of a bridge over the Wilhelmina Canal. Far more resistance was encountered than had been anticipated, and in the end, the Allied forces were overrun. Many troops were trapped because the bridges were not held, and they had to be evacuated. The exact number of casualties among the Allied forces is unknown, but there are believed to have been more than 15,000 dead, wounded or missing.

When one uses the phrase "a bridge too far," the implication is that such an unrealistic goal not only will not be reached, the result will end up being harmful in some way. For example, a company with an overreaching goal might end up going out of business. A person's or group's project that is too ambitious might have to be scrapped altogether when it cannot be completed, resulting in a waste of time, money and effort. A more realistic target would be much more likely to reach, and extending the goal too far might result in a disproportionate amount of unwanted consequences if success is not achieved.