According to Maslow, the unmet need is referred to as the prepotent need. He believed in the idea of fulfillment progression, which is that lower, more basic needs must be met before higher needs are activated. He used this idea to explain why hungry people would try to steal food even though they knew that there were serious penalties for theft. People are motivated by physiological needs before they are motivated by safety needs. The next higher level need (safety) is not activated until the preceding lower level need is satisfied (physiological). Individuals systematically satisfy their needs by starting with the most basic need that is prepotent and then working up the hierarchy.
For example, if a person's social needs are not met, then that person will not be motivated by esteem or self-actualization needs until social needs are satisfied. Maslow did recognize that there could be exceptions to this idea of fulfillment progression, but these were his basic notions.
The reason that Maslow arranged the needs in a triangular shape was because he believed that more people are motivated by lower-level needs (physiological, safety) than higher-order needs (social, esteem, self-actualization). In fact, he proposed that very few reach self-actualization. However, he did state that many behaviors can meet several needs at once (Feist & Feist, 2009). So for instance, an artist might create a painting. That behavior provides for the esteem need as the artist can take pride in his or her work, it may also provide for social needs as other people may strike up conversations with the artist about the painting. And lastly it can provide for the basic level needs as the artist can sell the painting for money to purchase food and shelter. However, Maslow stated that all individuals must eventually satisfy those lower level needs even though they can be put off temporarily to satisfy higher order needs. To extend our artist example, let's make the individual a "starving artist" if that person sacrifices food to make art, he or she will eventually have to eat or they will die.