The tweet annoyed me because there is nothing that bugs me more than people who can't explain what they feel and why. Having bouts of "inexplicable" sadness, happiness, joy or depression is the best way to manipulate others. Of course, there is always a reason why we feel things. There are people who are so emotionally immature that they truly can't explain to themselves or to others why they are experiencing a certain emotion. This profound immaturity is bound to manifest itself in many other respects, so I would avoid such emotionally stunted individuals at all cost.
Then there are those who love manipulating others by exposing them to a barrage of emotions they pretend not to be able to explain. "I just feel sad and I don't know why," is the best way to keep those who have the misfortune of knowing such an individual wondering if they might have caused this sadness.
So my advice to those who don't know why they feel what they feel: until you find an explanation, keep your emotions to yourself.
P.S. This silly tweet is a quote from Paulo Coelho who sold many books by being extremely pompous.