idiom "the main chance"

[Lost_Soul]

Hi, everybody !!!

What does this idiom mean? Could you give me a hint on it, please.

"His eye was on the main chance"

Thanks !

[Yankee]

Hi LS

I wouldn't say the whole sentence is an idiom, but rather only part of it:
to have one's eye on something
"to have seen something that you want and that you intend to get."
"to admire and want to have something."

http://idioms.thefreedictionary.com/have+eye+on

In the link above you'll notice that you can also "have your eye on someone".
"to watch someone carefully"

What or who "the main chance" might be depends on the broader context.

[Conchita]

Here's something for perspective:

have an eye to/for the main chance UK
Someone who has an eye to/for the main chance is always ready to use a situation to their own advantage.

(from Cambridge Advanced Learner's Dictionary)

have an eye for/on the main chance British & Australian
if someone has an eye for the main chance, they are always looking for opportunities to make money and to improve their situation:
She was someone who had an eye on the main chance and who never missed an opportunity to exploit others.

(from Cambridge International Dictionary of Idioms)

[Yankee]

Thanks, Conchita. I'd never heard that expression before. So I guess you might say "the broader context" here is British and Australian English.