Emotional stimuli, adequately sustained over time, can give birth to the sense of (say) romantic love, which is nothing more than an expression of our limbic system to continue seeing themselves subject to the necessary emotional burdens that balance and release of certain features preferred not our mood, and that reaction leads us to believe that a state of flux that we will uphold the rule of preference: Happiness found.
Thus, the mind sets the target and promote events or counter their achievement and preservation. The variation of the preferential status that makes the mind of the target, as a principle it induces the emotion trigger (or not) a sense that the motivation to act.
The most difficult part is knowing that they are governed by the laws that govern the functioning of the brain energy. EGO preferably inhibited by a sense equivalent to foster a yearning, a desire to delay or frustration promotes vehemence. Feelings need a reason or channel for us to feel satisfied and balanced.
Because all individuals express the same feelings in different situations, one can say that no two situations are the same or two people that show exactly the same intensity of feeling a common event triggered by them. Given this evidence, we can say without equivocation that humans are different from their fellows, as motivated and that people respond differently to the feelings of others, sometimes encouraging and other counteracting load.
Source : http://es.wikipedia.org/wiki/Sentimiento