golang でパニックが発生する理由は何ですか?

package main 
import "fmt" 
import "runtime/debug" 
 
func fun() {
    fmt.Println("fun begin")
 
	defer func() {
			//捕获panic
		if err := recover(); err != nil {
			debug.PrintStack()
			//获取堆栈信息的字符串
			fmt.Println("xxx", string(debug.Stack()))
		}
	}()
 
	var p *int
	//产生异常
	*p = 0
	fmt.Println("fun end")
 	//这里不执行
	for {}
}
 
func main() {
	fmt.Println("main begin")
	fun()
	//因为panic被recover捕获，所以下面继续执行
	fmt.Println("main end")
 
	for {}
}

main begin
fun begin
goroutine 1 [running]:
runtime/debug.Stack(0xc000088060, 0xc00009a000, 0xa)
        /usr/local/Cellar/go/1.11.1/libexec/src/runtime/debug/stack.go:24 +0xa7
runtime/debug.PrintStack()
        /usr/local/Cellar/go/1.11.1/libexec/src/runtime/debug/stack.go:16 +0x22
main.fun.func1()
        /Users/xxx/test/a.go:10 +0x46
panic(0x10a9760, 0x115d520)
        /usr/local/Cellar/go/1.11.1/libexec/src/runtime/panic.go:513 +0x1b9
main.fun()
        /Users/xxx/test/a.go:16 +0x7f
main.main()
        /Users/xxx/test/a.go:24 +0x66
xxx goroutine 1 [running]:
runtime/debug.Stack(0xc00007ada8, 0x10a9760, 0x115d520)
        /usr/local/Cellar/go/1.11.1/libexec/src/runtime/debug/stack.go:24 +0xa7
main.fun.func1()
        /Users/xxx/test/a.go:11 +0x4b
panic(0x10a9760, 0x115d520)
        /usr/local/Cellar/go/1.11.1/libexec/src/runtime/panic.go:513 +0x1b9
main.fun()
        /Users/xxx/test/a.go:16 +0x7f
main.main()
        /Users/xxx/test/a.go:24 +0x66
main end