Https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-algorithm-scripting/where-do-i-belong SOLUTION

I was working on this puzzle, and I got a working solution for almost all cases:

function getIndexToIns(arr, num) {
  arr.sort(function(a, b) {
    return a - b;
  });

  for (var i = 0; i < arr.length; i++) {
    if (arr[i] >= num)
      return i;
  }
}

I got a bit fed up, so I checked the solution: I see that, to deal with the other scenarios, the proposed solution returns “arr.length”. I don´t understand why, though. Could anyone explain?