Hey, Grandma Moses started late!
The balance is between having the aperture wide enough to let in enough light and retaining the depth of field you want (if that is an issue), and having the shutter speed long enough to let enough light in without camera shake or movement causing too much blurring.
And with ISO, having it high enough to be able to further reduce the shutter time but without becoming too grainy (unless you are after this look). Ad astra per aspera
