Recursive functions usually return a result built from the smaller result. The classic example is the factorial: 5! means 5 × 4 × 3 × 2 × 1. Notice that 5! is just 5 × 4!, and 4! is 4 × 3!, and so on down to 1! which is 1:

def factorial(n):
    if n <= 1:
        return 1
    return n * factorial(n - 1)

print(factorial(5))
print(factorial(10))

To trust a recursive function, you don't need to follow every call. Check two things instead: the base case returns the right answer, and if the smaller call returns the right answer, this step combines it correctly. If both are true, the whole thing works. That leap is the key to thinking recursively.