Lyric discussion by Leafsdude 

Cover art for Happiest of Days lyrics by Goo Goo Dolls, The

Sounds like a relationship with a person that suffers from depression. In that context, it's actually a very complex song lyrically. Among the symptoms of depression is overactive thoughts, which fits the first verse. I still hear the last line of each verse as "I know you're wrong, I know you're strong", which also fits with the general feeling of worthlessness depression brings. It can also be difficult for non-sufferers to relate and be supportive due to the often times random nature of episodes, sometimes without any obvious triggers, which fits a lot of the rest of the song: keeping to yourself to keep from making things worse after saying things like "just get over it". When you understand depression, and especially how sufferers cope, you learn that the best way to be supportive is to just listen.

In the song, it definitely sounds like the narrator said something dumb about it, and it's putting a major strain on their relationship, but they want to fix it. There's no doubt they have strong feelings for the person in question, especially when the individual is struggling on their own ("it's so hard to see you staring right past me"). There's actually a level of heartwarming in the line from the title ("while you're struggling through the happiest of days"), considering, as the thought that they consider their life happy, even as they struggle through a mental illness that makes them feel sad, is pretty sweet.

My Interpretation