Law of Marginal Utility
The individual preference ranking, or utility ranking, is central to economic action. Humans make choices and act on those choices in a spatial and temporal fashion. If an economic actor chooses activity A prior to activity B, it is clear that that actor prefers activity A over activity B, in that particular moment...in time. Likewise, if B is the next preferred activity, it is preferred over C and D. These activities are ranked from top preference, in an ordinal fashion, to the lower preference of activity. This process happens naturally, as the human mind processes this information.
Space and Time
Since we only have 24 hours in one day, things must be done in a priority fashion, as mentioned in the previous paragraph. However, time is a factor in scarcity. In fact: Time is the notion that creates scarcity. It is not resources. Another fact: so is space. Space is the other cause of scarcity. This is also true since we can only occupy one space at one time.
Time is a notion of our intuition. It is not something that is external to us, rather it is internal to us. This also goes for the notion of space. Space is a concept, along with time, that is vital to how the human mind processes things through the senses. Since humans are not demigods, and we do not possess the trait of omniscience or omnipotence, time and space becomes the restricting factors. It is our minds that create the scarcity. This does not mean that somehow we can expand our thinking to rid ourselves of scarcity, as this impossible due to the law of negation. This law impacts us spatially and temporally.
Example: Can a person be at the barbershop, but not at the barbershop at the same time? Of course not. Thus, the person must be at one place at one time. Since this concept is true universally, we must now deal with the law of marginal utility. One preference over the next, acting in time and space. This is how it works no exception. Staying consistent with the barbershop example, either we can go to the barbershop, or we can go to the movies. If the barbershop is chosen, it's clear, based on that decision at that time, the activity of going to the barbershop is preferred over the activity of going to the movies.
Time and Space are the causes of economic scarcity. As objects appear to us, these objects, or concepts, appear to us in our minds as things in space and we act upon them temporally. Since space and time are concepts of our intuition, we are limited on those things we can act upon during one moment in time and in space.