The principle of Hapkido is based on the principles of “Hwa”, “Won”, and “Ryu”.
When you have all of these principles, you can only say that is true Hapkido.
"The motions of Hapkido are going to be right when you use the circle, flowing and achieving harmony with your opponent; or, in harmony, using the circle, and flowing".
As this sentence says, It's not important which is used first; you should just use them together.
You also should use them not only as SoolKi(technique), but also breathing, falling method, kicking, hitting and arms-skill. You need to train yourself hard.
There are also differences in SoolKi, in accordance with the differences of level.
It also means the flowing of force when you are in the situation that you need to concentrate your force which is needed for attack.
it‘s repeated again, again, again...