When somebody is tickled, they laugh and tell you to stop at the same time. Explain this to me please!!!?

so i don't know why, but whenever somebody is tickled, they always are hysterically laughing but they are like "hehestop!hehestop!hahehastop!" so i don't understand it. They are laughing, but they like it and don't like it and sorta like it but i don't get it