Here's the scenario. I am an expert in a subject X and I would like to combine it with method Y to do something new. I have a distant connection to someone who co-authored a book on Y and I approached him suggesting a collaboration. He responded positively as X is interesting to him.
My collaborator then pulled in a PhD student to look at the problem but he was not good and nothing happened. He has now pulled in another PhD student but his work is equally disappointing. I think he must have spent a week putting together some really buggy code that does not do even the simplest version of X. In the meantime (about 2 months) I think I have learned enough about Y to be able to do the whole thing myself. So I am not longer sure if there is any value to me in the collaboration, especially as getting the students to do the work right may take longer than me doing it.
Would it be reasonable to ask to end the collaboration ?