[Deepurple]

While looking up a dictionary, I have always found the definition of a word can be both uncountable and countable. I would like to know the reasons why, and in what ways I can use them properly in essays?

To cite an example from Longman Dictionary:

Attachment
[uncountable and countable] a feeling that you like or love someone or something and that you would be unhappy without them

a child's attachment(uncount) to its mother
a romantic attachment(count)

As shown above, how can we know when the word be used as an uncount or count?
Why is that "attachment" can be defined as uncountable and countable under the same entry but falls short of providing any clues on their usage? Dear teachers, do you have any recommendations to resolve such a problem?

The greater details of the explanation, the better.
Thank you.