The end hook on a retractable tape measure is loose so that it should read correctly when
a) hooked over the end of a piece of wood and pulled tight
b) pushed up against an object when measuring from that object e.g. a wall

What you don’t want to do is just place so the end hook is somewhere between the two positions.

Thanks Simon. You articulated that better than I did.
I should have said that pushed vs pulled tape measurement can vary (eg: overly loose cleat, worn cleat rivets etc).
It's good to check the tape against a steel rule to determine if it's accurate in both directions, and check it periodically.

Side Note:
When I did carpentry as a teenage apprentice (back around the Dark Ages) the boss would get grumpy if you let the tape snap back against the casing! That's exactly how those little rivets get loose and holes in the metal tape get distorted!