The word conflict has mostly negative connotations when first considered and may describe a physical manifestation of a disagreement such as a war or may signal an impasse when a dispute cannot readily be solved. However, it can have positive results in personal development and character building as conflict potentially forces the relevant parties to explore each other's perspectives.
Fear, when considered alongside conflict, is an emotion often expressed in response to imminent danger or even the hint of a threat. As with conflict, fear has unpleasant or even life-changing implications, although fear is in fact a healthy response to a difficult or dangerous situation. When that fear is not managed or becomes irrational, it can lead to inappropriate behavior, a breakdown in communication, or even violence. In other words, fear may cause conflict. This statement is, however, flawed because there are other causes of conflict which revolve around control—not fear of losing control but determination to preserve control simply because power can be all-consuming. Therefore, the statement that fear is at the heart of conflict is very broad and requires much analysis because some would argue that fear grows out of conflict and not the other way around. The matter could be debated at length for all its implications. Sometimes the fear does not come from the conflict itself but from the potential outcomes of that conflict when people get hurt trying to resolve the conflict.
In literature, conflict can take on many roles and it always drives the plot forward. The definition of conflict in literature involves the clashing of ideals as characters strive for a goal and must overcome any obstacles en route or convert those obstacles into opportunities. Fiction writing needs conflict, which can be represented (for example) as man-against-nature, man-against-himself, man-against-society, and man-against-man. When considered under these headings, fear does have a large role to play in resolving conflict. There is fear of the future if one particular choice is made, such as in Eveline from James Joyce's Dubliners series, which manifests as man-against-self. Eveline's internal struggles against the forces of duty and fear are central to the belief that whether she stays or goes she will not be satisfied. There is Macbeth's fear in Macbeth when he initially resolves not to carry out the heinous deed that threatens to "unfix my hair" (I.iii.135) before he decides that he will indeed kill Duncan. Of course, there are any number of examples. Note that conflict in literature does require choices to be made and consequences to be witnessed so that the conflict can be resolved, whether for the good or bad of the situation. Therefore, those choices often revolve around fears.
There can be conflict in literature between two equally deserving choices, which would suggest that fear does not need to be instrumental in this type of conflict. However, regret may result from a poor choice and this may lead to a reluctance to make choices later for fear of making a poor choice. Consider Robert Frost's The Road Not Taken. The narrator reflects on what he may experience or what he has to forego in making a choice.
"at the heart of conflict is fear"
The statement is true in a very basic way because of how the words CONFLICT and FEAR are generally interpreted. THE POINT: both conflict and fear, like all concepts, are not specifically universally definable BUT WHAT THEY SHARE is an undesirableness. We do not want fear and we do not want conflict to last.
We may begin by deciding on the (subjective) definition of CONFLICT. A conflict is a struggle between two or more parties. It can be, but doesn't have to be, violent. We may compare conflict to, say, competition. All parties usually want a conflict to end, as it is painful by definition. Whereas competition, though maybe painful at times, is also generally meant to serve a COMMON goal, for example in market capitalism (educating, exercising, entertaining, etc.). So WE MAY DEFINE conflict as a painful competition that will likely only benefit the victor, and therefore any common goals are often re-prioritized in favor those goals that will bring victory. A longer conflict is disadvantagous only to the victor, unless there is a truce declared (in which case both parties pay the price for a longer conflict). The defeated might lose everything no matter the circumstance, so ANY conflict is not in his/her/their favor.
By HEART of conflict, we may mean the original CAUSE of a conflict or the cause of the conflict's perpetuation. We may also mean the emotions that dominate the personal interactions which occur during conflict (whether they be between "enemies" or "allies", the latter are not always in agreement amongst themselves and may use fear to suppress dissention, for example).
FEAR is a negative emotion. The word is very much indescribable, like the color blue. It might be for that very reason that the word fear effectively conveys a "feeling" from person A to person B when exchanged in language. How does a person having fear act? It depends on the individual. How does a person having fear describe how they feel? It depends on the individual. Fear, though, it is generally agreed, is something that EVERY individual does not want to have if it can be avoided.
SUMMARY: "[...fear is] at the heart of conflict...]" generally because a conflict is DEFINED to be disadvantagous for as long as it is ongoing. Fear is, by general definition, so inherently disadvantageous that it might generally be considered to be disadvantage itself. "The only thing we have to fear is fear itself." FDR was stating that fear is, literally, disadvantage. With conflict comes disadvantage.