If you’re researching a family with a name like Jansen, Zwiers, or Pieterse, at one point you will find the original person for whom the name was not a hereditary last name but a patronymic derived from the father’s name.
My mother’s name is Marijnissen. As a beginning genealogist, it took me a while to realize that the father of her brick wall ancestor wasn’t called Marijnissen but had Marijnis as a first name. I found his father as Marinus Peeters.
When dealing with such names before 1811, you should always test both possibilities: that the father used the same last name, or that the father used a first name from which the patronymic of the child was derived.