We have emotional immune systems that have a lot in common with our physical ones. Kids get sad, angry, or happy easily, but they are also constantly taking in new experiences and learning what to watch out for. Adults are more stalwart and set in their ways. Adults have resistances to emotional threats, but they can’t adapt as well as kids can. It’s good to get chicken pox when you’re young, and it’s good to face emotional threats (safe ones, of course) when you’re young, to build resistance early.
Therapy is about regaining the resiliency you had as a kid. In order to do so, you have to set aside the resistance you’ve built up. It’s risky to shut down your emotional immune system in public - I bet you’ve met people who have been so raw and open, and felt concern for them - so a private, confidential place is necessary. In therapy you safely work out which parts of your resistance protect you and which are no longer needed. You also find out what new kinds of resistance can protect you, which is very hard to do when your immune system is already in place.
The tricky part is that it’s impossible to just completely set aside your emotional immune system as though it had an Off switch. When you power it down, little by little, the system gets agitated - as it’s supposed to; it’s trying to protect you, and doesn’t always know whether something is a threat or not. Therapy is about building a space in which you can power the system down at will without setting it off.