This is the opportunity 'of a lifetime'. = This sort of opportunity comes along 'once in a lifetime'. [=this is a very rare opportunity]
a baseball player's 'lifetime' batting average [=batting average measured over a baseball player's full career]
She was presented with a 'lifetime' achievement award. [=an award for all the work she has done in her life]
(..) hungry know who's to blame. Have you ever sowed the field, Lady Olenna? Have you ever reaped the grain? Has anyone in House Tyrell? A lifetime of wealth and power has left you blind in one eye. You are the few, we are the many. And when the many stop fearing the few... (..)2015 TvShow: Game of Thrones Title: The Gift Season: 5 Episode 7