In a very tangible sense... I could compare it to my perspective on my work schedule. I prefer to work days, early hours, and be off on Saturday, and have let my employer know all of this. Usually that works out fine. But I used to dread checking the new schedule postings for fear that my schedule would deviate from my expectation. At some point I realized how much stress that was causing me and tried to work on coming to it in a different state of mind. Now I try to come to it with a sense of equinamity. I still hope that I get my preferences, but I don't automatically assume I will be miserable if I don't get them. For example, I'll be working tonight instead of this morning, because a coworker needed to switch, but it's ended up working out really nicely because I'll get to spend the day hanging out with my boyfriend, and it turns out he has a family engagement tonight anyway. It actually is even better than working the day shift. I still struggle with not feeling deflated when I see a less-than-preferable schedule, but I feel more in control and at peace now. It's more like I can create my own happiness instead of relying on events to create it for me.
I'm hoping to carry that sense with me when I go into a new career. Whenever you start something new you're bottom of the barrel, so I know I'll have less-than-preferable duties and hours. But I often end up feeling that my sense of disappointment is far worse before an unpreferable event than during the event itself - usually during I'm engaged in whatever tasks I'm doing, and cognitive distress just isn't useful. So I'm going to try hard to carry that sense of "everything will work out just fine" with me. That trust opens the floor up for me to take control of my personal happiness instead of assigning it to some external variable.