One of my mares is like a perpetual teenage girl. You know, the kind that if you come around a corner and say something she screams and drops her sandwich on the couch? She is like the teen who can be half asleep for most of the day, then hyper/excited at all the wrong times. Just like a girl, she relies heavily on peer pressure to know what to do. "Are you guys scared of that or what? If everyone wants to run, I do too!" Like a teen, she will stay out of trouble when with a group of mature individuals, but get her in the wrong crowd and you better keep an eye on her. Whatever you do, don't let her go out with another silly teen or you will be sorry. She's also boy-crazy and bats her eyes at every gelding she sees.
My other mare is like a new police officer just out of training. When she's getting ready to go to work she's so excited she can hardly stand it and needs to have a mature partner help her calm down and get her head into the work for the day. As long as she's with a reliable partner she does an excellent job in most situations. However, when it comes to a big sting or riot situation she's liable to lose her head and over react. Her partner always has to keep an eye on her to make sure her guns don't go off, and sometimes she has to be talked down.