how to interpret brains, chances, etc..

[slim1111]

As a student of the english language whose native tongue is of an asian language, I have trouble with understanding many plural forms of words
that are not intuitive to me.

Examples like book/books are easy enough to understand since
they are countable and we can see how to count those words.
However, in case of words like brains, chances, congradulations, forces
and such, it is a bit harder to grasp what they mean when used in
a plural form. For example, the word "chances"
It seems to me people often use it like

"what are my chances of winning?"

if the word chance were to used as a winning percentage, I see no reason
why it should be pluralized. why shouldn't it be

"what is my chance of winning?"

Same with the word "brains". Of course we can
have two brains if there are two people, but it seems like its meaning
is a little different when used in its plural form.

Please enlighten this poor soul who's been struggling and laying awake
countless nights.

Thanks in advance

[Tdol]

You could say 'What is my chance...', but we use plural numbers to calculate chances/odds etc- 10 to 1, 50-50. etc, so the plural makes sense to me.