Okay, so you know how sometimes, when you're feeling upset or sad, it's hard to put those feelings into words and explain why you feel that way? Well, Claude Steiner was a man who wanted to help people understand their feelings better, and communicate with others in a way that was kind and respectful.
He came up with something called "Transactional Analysis," which is basically a way of understanding how people interact with each other. Think of it like a game of soccer - there's the person with the ball (the "sender"), and the person who wants to take the ball (the "receiver"). And just like in soccer, there are rules for how people interact with each other in everyday life.
One of Claude Steiner's big ideas was the concept of "strokes." No, not like petting a cat - in this case, a "stroke" is any kind of attention or recognition you give to another person. You can give someone a "positive stroke" by telling them they did a great job on something, or a "negative stroke" by criticizing them. If someone doesn't get enough strokes (or they get too many negative ones), they might start to feel bad about themselves.
Another important idea that Steiner had was the "OK Corral." Basically, this is a way of understanding how people see themselves and others. Imagine a square with four corners: the "I'm OK, you're OK" corner, the "I'm OK, you're not OK" corner, the "I'm not OK, you're OK" corner, and the "I'm not OK, you're not OK" corner. The goal is to try and stay in the "I'm OK, you're OK" corner as much as possible, because that's where you have healthy, positive relationships with others and with yourself.
So in short, Claude Steiner was a person who came up with ways to help people communicate better, understand their feelings, and have healthier relationships with others.