Thank you all.
I found this a phrasal exmple of the phrased "a fly in the ointment" in the Collins Cobuild Advanced Learner's English Dictionary. I wrote this in a piece of paper to ask you later but since I was very sleep, it is hard for me to attest to the accurate transcription of the example spelling by spelling, but here it is:
If you describe someone or something as a fly in the ointment, you think they spoil a situation and prevent it being as successful as you had hoped.
I feel the past perfect 'you had hoped' is correct but can't lay out the reason or reasoning involved. Can you help?