Not so adults. Why? Maybe we are obsessed with our work or home pressures, career progression, or an unsatisfying job (assuming we work for someone). But then, you see lots of people who are generally able to smile through anything, and even laugh at themselves and life.
No idea how they do it, but these kinds of people are a joy to behold and be with. In films too, my favourites were the happy-go-lucky people (yes, I know they were acting) who exhibited a devil-may-care attitude, or a mischievous demeanour, in a nice way. Dev Anand comes to mind (his autobiography is titled Romancing with Life), and so do Shammi Kapoor and Kishore Kumar. And Madhubala in many of her roles.