There is another thread with exactly the same question, but the vid answer is not available.
Here was the question from another thread:
I use Extrude command to make object on the surface of another object, and after I draw the profile on the surface and accept, they request to choose "non-symetric extent" or "symetric extent", and "through all", "through next", "from/to extent" or "finite extent".
But after I choose one side and enter the dimension, they ask me to enter the dimension of opposite side. But I don't need the opposite side.
So how can I choose only one side to make prominent object?
I can only assume that you are using Ordered modelling. In which case it would appear that you have at some time previously set the command bar to Extrude - Non symetric extent. As these commands are modal it will remain set what ever way you last used it.
In this case the the Non-symetric extent is highlighted.
To 'fix" this issue simply click on the highlighted icon and it will return to the simple extent mode.