Like geniegal, the title of this thread raises some questions for me.
Here they are. You'll have to answer them. Some may not apply, others might, that's up to you to consider. Some are kind of repeats of others, in slightly different terms. I'm just trying to give a broad selection so one might hit a button and help you sort out the issues.
Why is it childish to trust things to work out for the best?
Why do adults have to work at jobs they hate?
Why is risk-taking a childish activity, as opposed to an adult one?
Why is being angry and dissatisfied a sign of adulthood?
Are adults automatically mature or have they just lost their ability/desire to take risks?
Why is it wrong to be childlike (not the same thing as childish!)?
Why does being an adult mean you have to be unhappy?
Why is trust incompatible with adulthood?