Noun
(obsolete) A venture which stands the best likelihood of success; a risk; fortune (of a person, country etc.). [16th–18th c.]
(archaic) One's primary interest in life; livelihood, especially an opportunity to benefit oneself. [from 16th c.]
Source: en.wiktionary.orgI know what's what, and have always taken care of the main chance. Miguel de Cervantes
... the fear of God together with a keen eye for the main chance. Ralph Barton Perry
Behind a leader there must be followers, but they should always be on the lookout for the main chance and ready to change sides if the current leader doesn't deliver. Mary Douglas
Good soldiers stay alive by being unsentimental and having a quick eye for the main chance. Michael Shea
R. Lyne, Augustan Poetry and Society, 599 On the other hand, the poet has been unsympathetically described by one scholar as "a sharp and rising young man, with an eye to the main chance." Source: Internet
Strabo VII.3.11-12 The coalition's main chance came in 62 BC, when the Greek cities rebelled against Roman rule. Source: Internet