Most young people starting out in the workforce are miserable because they’re not working for their dream company or doing exactly what they’d like with their career. Sometimes this stage in your career is where you learn what you want to do or the types of people you want to work with. The process of elimination can be useful early on in your career.
-Ben Carlson, as copied from here
The heading says "mostly" because of the second sentence. My first three jobs in the three years after I graduated from college were house painter, grill cook and sandwich maker, and a newspaper deliverer. I don't remember ever being miserable.