Thank you for your question. Having a good opinion of God means that a person trusts God to do what is better for them. If a supplication is not answered, and if the person has actualized all of the conditions for their supplication to be answered and has acted with wisdom, then this is the stage in which a person needs to have that good opinion. So there isn't a dichotomy between unanswered prayers and our opinion of God, as a good opinion is not dependent on the answering of certain prayers.
May you always be successful.