First, to merely de-activate your account Facebook confronts you with a psychological manipulation to get you to avoid doing that.

deactivating your account is still a complex process. Go into your settings and click General. At the bottom, you’ll find Manage your Account. From there, click on “Deactivate your account” and type in your password. Before you’re completely off the hook, Facebook shows you photos of all the “friends” you’ll miss (“Callie will miss you”, “Phoebe will miss you”, “Ben will miss you”) followed by a survey asking you to detail your reasons for leaving.

And deleting your Facebook account is extraordinarily well hidden. Facebook tries very hard to prevent you from deleting your account.

Now, to permanently delete your account, you’ll need to learn where the delete option resides. The easiest way to find it is by clicking the “Quick Help” icon in the top-right corner, then the “Search” icon. When you see the search field, type “delete account.” You’ll see a list of search results. Click on “How do I permanently delete my account?” and Facebook will give you the obscure instructions to “log into your account and let us know.” In this case, “let us know” is code for “delete my account,” so click on that link.

But this does not actually delete your account. It’s a sort of a suggestion to Facebook, you see. Actual deletion takes place days later and if you should happen to inadvertently log back into Facebook during this period, the account deletion is completely suspended.
Source: How To Delete Your Facebook, Twitter, Instagram, and Snapchat | WIRED
Everything about Facebook is about psychological tricks and manipulation of its users.