"simple" question about a function

I am on lesson 101 of Javascript. I’m SO close to finishing the basics (although I’m probably going to need to keep peeking back and forth at it). But I don’t understand one of the things its saying here.

"Recursion is the concept that a function can be expressed in terms of itself. To help understand this, start by thinking about the following task: multiply the first n elements of an array to create the product of those elements. Using a for loop, you could do this:

  function multiply(arr, n) {
    var product = 1;
    for (var i = 0; i < n; i++) {
        product *= arr[i];
    }
    return product;
  }

However, notice that multiply(arr, n) == **multiply(arr, n - 1) * arr[n - 1]** . That means you can rewrite multiply in terms of itself and never need to use a loop."

Now what I’m not understanding, is where does the (n - 1) come from at the bottom where it says multiply(arr, n) == **multiply(arr, n - 1) * arr[n - 1]? I thought it would be n + 1 since statement 3 in the forloop is that i increases by 1 each time.

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With recursion you need to ‘count down’ to a smaller case by reducing your input each time so that you can reach a base case. Reaching the smallest possible input is how your code knows to stop calling itself.