Experience more than one wants to, learn a hard lesson; also, see combat, especially for the first time. For example, After the expedition lost two climbers in an avalanche, they had seen the elephant and turned back, or On his first tour of duty he saw the elephant. This slangy expression, first recorded in 1835, alludes to having seen all the sights one can see, including that rare beast, and returning home unimpressed or disappointed.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.