[Grammar] Opportunity

[Takoyaki]

Hello

"Opportunity" can be used as both a countable noun and an uncountable noun, but how can I decide which one to use when I use it in a sentence?
I mean when it is used as a countable noun, we need "an" before it, so it is very confusing.

 

[Heterological]

A specific situation is "an opportunity," for example, a job opening (we have many opportunities here at XYZ Enterprises!) As an abstract concept, it is the non-countable "opportunity," as in Edison's quotation, "most people miss out on opportunity because it is dressed in overalls and looks like work" (or something to that effect.)