Go并发编程中，通道接收数据的顺序为什么不是goroutine启动的顺序？

<code class="go">package main

import "fmt"

func sum(s []int, c chan int) {
    sum := 0
    for _, v := range s {
        sum += v
    }
    c <- sum // 将计算结果发送到通道c
}

func main() {
    a := []int{7, 2, 8, -9, 4, 0}
    c := make(chan int)
    go sum(a[:len(a)/2], c) // 启动Goroutine 1，计算前一半切片的和
    go sum(a[len(a)/2:], c) // 启动Goroutine 2，计算后一半切片的和
    x, y := <-c, <-c       // 从通道c接收两个结果
    fmt.Println(x, y, x+y) // 打印结果
}</code>

<code class="go">package main

import (
    "fmt"
    "runtime"
)

func sum(s []int, c chan int) {
    sum := 0
    for _, v := range s {
        sum += v
    }
    c <- sum
}

func main() {
    a := []int{7, 2, 8, -9, 4, 0}
    c := make(chan int)
    go func() {
        fmt.Println("Goroutine 1 ID:", runtime.GoID())
        sum(a[:len(a)/2], c)
    }()
    go func() {
        fmt.Println("Goroutine 2 ID:", runtime.GoID())
        sum(a[len(a)/2:], c)
    }()
    x, y := <-c, <-c
    fmt.Println(x, y, x+y)
}</code>