Can some one explain the end of my fibonacci code?

Question

I was creating fibonacci and my original return was "return (num - 1) + (num - 2)" but dont work, some one sugested to call the function "return fibonacci(num - 1) + fibonacci(num - 2)" and it worked, my question is why?

Code in anex

function fibonacci(num) {
    if (num < 2) {
        return num;

    } else {
        return fibonacci(num - 1) + fibonacci(num - 2)
    }
}

Answer 1

I see in the MDN, "The act of a function calling itself, recursion is used to solve problems that contain smaller sub-problems. A recursive function can receive two inputs: a base case (ends recursion) or a recursive case (resumes recursion)." Thanks for the pacience to explain Parag Diwan.