Is it true that happiness can only be attained by following our passions? No, it is not necessarily or always true. It's isn't always true when, going passion after passion, we may still find ourselves unhappy. It is a cycle of endless desire. Passion is not the only thing that fuels life, and thinking so may indicate a narrow mind.
Seeing passion as life's ultimate goal is problematic when it comes to other people and other circumstances that need to be considered. Harmony, like passion, is very important not only as an aspiration, but to happiness as well.
Let's say there is someone whose passion is listening to loud music all the time, and that person lives in a neighborhood with other people who prefer quiet and serenity. Let's also say that without extremely loud music, the person becomes bored, meaning unhappy and unsatisfied. Let's say they refuse to compromise for headphones.
One day, after giving up on accepting this reality of living, the person's neighbor has had enough with the music. Not only does he hate it, he becomes so annoyed that he can't focus on his job—he's too busy being anxious about going home—to the point where he is fired. Now, the neighbor is unemployed, and all because of the person with a huge appetite for loud music. The neighbor knocks on the person's door, but the person can't hear the constant knocks because they're too busy listening to a special song they really like.
Eventually, the neighbor can't take it anymore and calls the police. Shortly after, two police officers fine the music-loving person with such a heavy fine that they can't pay their rent, which is due tomorrow.
Now, to answer your question: The guy followed his passion: listening to loud music. He still refused putting on headphones all the way to homelessness. Is he happy now, knowing he might be kicked out of his apartment—because of his passion?
You see, there are other things besides passion that are required for happiness and well-being. I'm not saying it's bad to follow one's passion, I'm saying that life is much more than the individual quest for happiness, and the things that reside in the wide zone may have a huge impact on that happiness, for good or for bad.
Your passions could get in the way of other people's passions, which is a problem because none of you live in a vacuum. We cannot therefore discard the existance of other people if we want to live in happiness. People might need to consider us as well, if we want to live in happiness. That is, of course, unless you live in the wilderness.
You could live both as a hermit and a thief, like Chirstopher Knight, who survived 27 years in that position. However, how can you expect to be satisfied for the long term when you are under the constant threat of getting caught by the authorities?
The problem I find with what I call Reckless Individualism or the "I-Don't-Give-a-Damn-ism" is that it is so narrow-minded, and having a narrow mind is the exact opposite of wisdom: why should I care about other people's suffering if I am better and more important than them? That is the headline of this popular approach to life. It's an approach that could led to the deaths of those who need more considering. Like the weaker layers of society. Like the sucidial. Our decisions have an affect on the outside world. We need to care, or extreme situations were people will kill themselves, will only increase. The biggest asset of reckless individualism is apathy. Apathy can traumatize, and traumas can lead to mental health issues.
Wisdom is all about looking at the big picture and minding every aspect in that picture, and each of their relations to other aspects. Some people, I guess, lack the intellect, empathy, or both, to do it. Most, perhaps.
I assume that if the person in the scenario I gave would mind the presence of other neighbors and their potential reactions to the person's passion for music, they would be able to compromise for the big picture that is the building they live in, and then no harm—or minimal harm—would be made (and of course they would have the money to make ends meet if they were just way more considerate).
One can be happy even if they do not pursue their passion—other things in which they do not have that much passion for can make them happy regardless of their passions. I may want, for instance, to eat a candy. But no—the candy is not healthy for me. But it's my passion. Perhaps if I ate something healthier I would be happier regardless of my passion for candies?
Besides, there is the criticism that passion isn't happiness, but a type of misery. It is known as the passion trap. Our passions may make it difficult for us to accept the present. And as long as we do not accept the present, we can't be happy.
Are those who feel passion in their hearts automatically considered as happy people? Let's say that one's passion is drugs. They are so passionate about them that they become addicted, and when they cannot take a dose, they become depressed. Even if they would take a dose and thus have the sensation they seek—they are well aware that they are in an infinite loop; a depressing loop that borders on despair… This is an example where following one's passions does not bring happiness, but the exact opposite.
Ultimately, there are two conclusions from all of this: Passion alone is not always sufficient in the pursuit of happiness, and there are some passions that could lead to the exact opposite of happiness, even if they may give us short-term satisfaction beforehand.
Thus, other factors should also be considered in the pursuit of happiness, from having good health to avoiding justified, yet avoidable, punishment.
Please note: I am not saying you should not follow your passions at all. I am only saying that there are also other factors and circumstances to consider, so that the pursuit of your passions does not become an unnecessary double-edged sword.
Either way, the philosopher can never be truly satisfied. As long as they are looking for wisdom by philosophizing, they will, never, be satisfied, completely. It's because you're always looking for something you lack.