I was reading the Mac OS X Lion upgrade page, and it said "make sure" all over the place. It struck me as odd. Where does the term "make sure" come from? What are you making to be sure? Yourself? Shouldn't the expression be, more verbose, but more accurately, "make yourself sure", or something similar?
"Make sure" here is a command means "Be sure" or "Be certain" or in a single word "Ensure".
It does not mean "make yourself sure" but "be certain that". But you can easily replace "Make sure" in your link with "Ensure" and all of it means the same.
Interestingly the origin of ensure is attributed to "make sure".
late 14c., from Anglo-Fr. enseurer , from en- "make" + O.Fr. seur "sure," probably infl. by O.Fr. asseurer "assure."
This link offers
Both assure and ensure came into English in the late 1300s, assure from Old French asseurer, “to reassure, calm, protect, to render sure,” and ensure from Anglo-French enseurer, “to make sure.”
A little more digging gives the Latin word
which means "To make sure or safe"; to assure
from Vulgar Latin *assecurare, to make sure : Latin ad-, ad- + Latin scrus,
So it has quite an old history in the form "make sure" derived from a single Latin word
"Sure" means "certain", and is interchangeable. Although idiomatically "sure" is more often used to refer to a state of mind, it doesn't have to be.
You are both making it certain that Tab A is in Slot B and also making yourself certain that Tab A is in Slot B. Presumably if you have done the latter you have also done the former, so it isn't necessary to distinguish between them.