Reciever/distance
Your aircraft should be close enough to you so that you can easily note the attidude and orientation of your plane at all times - at that range, unless there is a fault somewhere you will never have a range problem.
A FAQ from people new to the hobby is "how far away can it fly?" -and we all know the answer - further than you can see!
I learned to fly over a wheat field and had a real wake-up call when I moved to the UK flying in a small field surrounded by trees. But.......it has improved my flying!