When they are not offered you can still use them, but acknowledge them. Or you can still use them but transform the work into your own words. That is acceptable if it is not too close. If it is too close, then it has to be acknowledged. Plagiarism is the enemy of all writing.
Influence is the friend of all writing.
Once again, it's a value judgement. Writers have to learn to trust themselves. This Winter Night Night a mysterious, tangible presence that Shadows walking strangers. The air full of iridescent freckles atoms expressing infinity by falling and further further falling My dog carries the stars on her back. This is a revision that may or may not be my final draft.