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]
(..) Such a list does not exist. They are not an organisation in the sense we know. Nothing holds it together but an idea. There is no possibility of change in their lifetime. In the face of the Thought Police, they cannot act collectively. Individually, they cheat, forge, blackmail, (..)1984 1984