Stolen credit

Taking credit on someone else work is a delicate yet challenging social problem. It is especially more difficult in casual settings where no tangible benefit is visible at hand. In my opinion, a work is a work and the recognition thereafter, regardless of how important or unimportant it might become, should be respected and treated as such. If I need to use someone else work, I will always give credit to the owner; more so if I don't have any contribution in it, more so if it looks as if the work is mine, more so if I have a personal relationship with the owner, and even more so if it is a help to me.
But, somehow, some people don't share the same view as me. I am not a saint. So, I must say I was irritated. I felt betrayed. And, every time this kind of problem arises, I do not happen to tackle it as aggressively as I think I should have. It could be due to my shyness. It could be due to my modesty. Or, it could also be due to the intrinsic difficulty of the problem. I said the problem is especially difficult if there are no tangible benefits. It is because if I take on it aggressively, I might ruin my reputation more than that I could have built from the recognition. So, usually, I just keep quiet, more or less. This time, again, I kept quiet, more or less.

Addendum: Well, I guess I will need to tone down the "always" qualifier in the sentence: "If I need to use someone else work, I will always give credit to the owner". I just realized that in one of my assignments, I too adapted an algorithm I found online without citing it (ok, didn't think of citing it is more accurate). Although I have conscientious reasons for not doing so, I think it is still a mistake on my side. So, I shall take this as a "karma".