Determination is the “FATE Points” (hero points, Karma, what have you) of Icons, the resource that allows players to exert some influence over the otherwise random elements of the game and to directly affect the narrative. It is also a tool for the GM in handling things like disadvantages (the bad side of aspects in Icons), awarding players Determination when they come into play, as opposed to the more front-loaded approach of awarding addition build-points or character creation/design advantages.
Use of Determination is moderated by two things: certain requirements placed on certain uses—such as the limits on Determined Effort—and the need to tag Qualities.
Qualities, for those who haven’t read Icons (go ahead, I’ll wait…) are descriptive elements of the superhero, like “World’s Mightiest Mortal” or “Dark Knight Detective”. You need to “tag” or activate a Quality in order to spend Determination. In essence, it’s not just enough to say you’re spending X points, you also need to say what is enabling you to spend those points in this particular situation. What is it about your hero that is making this action special or important?
In other words, Qualities actually limit the use of Determination. While it’s often pro forma for players to come up with a way to relate their heroes’ Qualities to any given situation (how often does “Man of Steel” not apply to a superheroic action?) it’s still limiting. Another approach to Icons game play, more in line with previous generations of RPGs, is to ignore Qualities altogether. Just let players spend Determination on whatever actions they want. Other limits remain in place, such as the requirements for applying Determined Effort, although you can loosen them as well (see Determination Variants on the Icons Wiki for some examples).
You’ll probably want to keep Challenges as they are, since they provide a valuable source for acquiring Determination and a key way of handling character disadvantages and drawbacks; Icons doesn’t provide an alternative way of modeling superhero weaknesses, for example.
Why eliminate Qualities in Determination spending? It’s simpler and allows players to spend Determination in play more freely, without having to consider a meta-story reason for it. Plenty of RPGs get along just fine with such an approach, assuming that if players want to spend the points, they should be able to, no justification needed, no questions asked. (Hmmm, “Justification Points” would be an interesting name for an Icons mechanic…)
Freeing Determination from the Quality requirement can make Icons a bit friendlier to new roleplayers, who are already keeping track of the various other mechanics of how to play the game. You can introduce Qualities back in later on, just be aware that you’re limiting Determination use by doing so, rather than enhancing it, unless you’ve also made Quality-free Determination spending less effective in some fashion (half the normal bonus, for example). You can even mix the two: having the normal Quality-tagging Determination and an unlimited form of Determination spending that provides a lesser bonus (+1 per point rather than +2) for those occasions when inspiration doesn’t provide a good connection between Quality and action.