During free time, you can hang out with available characters in order to unlock new skills or skill points. After spending time with them, it prompts you to either give them a present or not.
Obviously, when you give them a present they don't like, the game makes you know that they didn't like the present at all. But sometimes, the event still triggers, providing you with either a skill or a skill point, and a big sigh of relief.
And sometimes, when you hear a success sound after giving a present, it skips back to your room without anything earned, except a moment of frustration.
Why would that happen?
Additional information: none of the characters is maxed out yet
Edit: I found out on the DR wiki that sometimes, some characters are in depressed mode, and if you engage conversation with them, you can spend time with them, give them a present, but it will only cheer them up. I looked at the table, and I can confirm I wasn't using free time on a depressed character.