Does considering someone's work regarding a piece of literature constitute plagiarism if you knowingly derive/spark ideas from it and don't cite it?
Why not cite things clearly if you know where your own idea 'derives/sparks from'? Laziness? Shyness? 

Citing somebody else's work won't diminish the quality or significance of your own contribution, on the contrary. 

And readers will be able to understand your foundations and line of thought better as a result.

And ultimately it saves you a lot of headaches, as you don't have to worry if you should - have - cite(d) other people's work that stimulated your thought.