Gouroutine个数问题

一个简单的测试，不太懂这里为什么 goroutine 个数始终为2，主线程跟 goroutine 应该不能算在一起?不太懂

package main

import (
    "time"
    "runtime"
)

func main(){
    go func(){
        for {
            select {
            case <-time.Tick(time.Second):
                print(runtime.NumGoroutine())
            }
        }
    }()
    time.Sleep(time.Minute)
}