OK…
Early in design, the intent was that all attempts to move an asset required a choice to move boldly or move subtly. But during early concept testing, it became apparent that this wasn’t working quite as intended: there were situations where neither option really fit.
Thus, the structure of moving was changed so that basic movement didn’t require a test, but characters could choose to take a risk with a ploy of being subtle or bold to gain an additional, valuable benefit at the risk of stalling your own progress (you can’t spent Momentum to move further, and you can’t keep the initiative) and giving an opportunity to the enemy. Indeed, the penalty for failing one of these ploys was made more severe here as part of this restructure.
These ploys have a base difficulty of 2 because that was the right break point for the risk and reward available: a base difficulty of 1 was too easy that the risk became too trivial, while a difficulty of 3 or higher made the reward too costly to reach.
However, as with all test difficulties in the game, it can be modified by circumstances, and these circumstances are typically represented by Traits (which include Assets, as Assets are essentially a sub-category of Trait).
The same also applies to the basic move: a trait that makes things more difficult could reasonably be applied to make an action require a test when it normally wouldn’t, or to prevent you from attempting some actions at all. In a skirmish, an obstacle or area of difficult terrain might be applied this way, making movement more difficult as you move along a particular route.