Simplified explanation of interface in Golang

Interface

package main

import (
	"fmt"
)

// INTERFACE IS A ACTION
type marathon interface {
	satisfaction() int
}

// STRUCT IS A PERSON WHO DOES ACTION. DESCRIBES THE QUALITIES OF THE PERSON.
type runner struct {
	endurance, persistence int
}

//FUNC SHOWS A WAY TO PERFORM ACTION
func (r runner) satisfaction() int {
	return r.endurance + r.persistence
}

// HELPER FUNCTION MEASURES THE ACTION
func measure(m marathon) {
	fmt.Println(m)
	fmt.Println(m.satisfaction())
}

func main() {

	m := runner{endurance: 5, persistence: 8}
	measure(m)

}