Three different thoughts about a missing file
1Yuna is preparing an audio project today. She cannot open a protected folder because she does not know its password. She says, "I wish I knew the password." Her friend asks whether she once knew it and forgot it. Yuna explains that she is talking about her present situation. She wants to know it now, but she does not. The sentence is not a report that she knew the password yesterday.
2There is a second problem. Yesterday, Yuna changed the main audio file without making a backup first. The new version has a mistake, and the old version is no longer available on her computer. She now regrets that choice. "I wish I had made a backup yesterday," she says. This does not mean that a backup is hidden somewhere. In the situation described, she did not make one. Her wish cannot change that completed event.
3Yuna has already sent a message to the technician asking for the password. She hopes that the technician replies soon, because a reply is still possible. Meanwhile, she writes a rule for her next project: make a separate copy before changing the main file. Her friend suggests writing all three thoughts in one list. Yuna labels them present difficulty, regret about yesterday, and hope for a future reply. The labels stop her from treating every past verb form as a report of a past fact. They also help her explain why knowing the password now would not create the backup that she failed to make yesterday.