In human behaviors, struggle is a term that typically refers an uphill climb, movement through a path of resistance, or activity in adversity.  In 1798, English economist Thomas Malthus argued that life is a struggle for existence; this logic was taken up by English naturalist Charles Darwin in his famous 1859 Origin of Species (chapter three: “Struggle for Existence”); and in 1886 Austrian physicist Ludwig Boltzmann, a fan of Darwin’s theory, famously propositioned that life is a struggle for entropy. This proposition soon came under attack and more theoretical or rather thermodynamic struggles soon began to be proposed. Some of these various “struggles” and are tabulated below.
Struggle | Free energy or entropy
There may be a German-to-English translation issue, on whether Boltzmann, in his 1886 paper "The Second Law of Thermodynamics" stated that life is a 'struggle for entropy' or life is a 'struggle for free energy', as there seem to be numerous citations for both cases, particularly after the publication of Boltzmann's 1905 book Popular Writings? (which seems to simply contain a reprint of his 1886 paper). As the term free energy was only coined in 1882 by German physicist Hermann Helmholtz, it is difficult to image that Boltzmann would be so comfortable to postulate this newly coined term as the essential quantifier of the struggle for life? Boltzmann does, however, cite Helmholtz and discuss energy set free in the context of chemical affinity. Boltzmann states, for instance, according to the 1974 Springer English translation, “It is a fact that when two like or unlike atoms combine in certain ways, very considerable amounts of energy are set free”, but nowhere is the term 'free energy' to be found. Neither is the term ‘free energy’ found in the 1995 book Ludwig Boltzmann: His Later Life and Philosophy, 1900-1906.  Neither is the term ‘free energy’ found in the 2006 book Ludwig Boltzmann: the Man who Trusted Atoms.  It is possible that Boltzmann never even used the term ‘free energy’ (or freie energie) once in his life?
The following are related quotes; some of which possibly being German-to-English technical mistranslation:
“Life, being that food and room are in limited supply, is a struggle for existence.”— Thomas Malthus (1798) 
“The general struggle for existence of animate beings is not a struggle for raw materials – these, for organisms, are air, water and soil, all abundantly available – nor for energy, which exists in plenty in any body in the form of heat Q, but of a struggle for entropy S, which becomes available through the transition of energy from the hot sun to the cold earth.”— Ludwig Boltzmann (1886) 
“Strife is not for the component substances, for these component substances of all organism, as air, water, and earth, are abundant; neither is the strife for energy as such, for this occurs in abundance, as the heat content of matter of our environment; but strife is for the free energy available for the performance of work.”— Walther Nernst (1893) 
“[The] struggle for existence is a struggle for free energy available for doing work.”— Ludwig Boltzmann (1905) 
“The whole web of life … is a struggle for free energy, whether it be between shrub and tree for a place in the sun, between a locust and a rabbit for the energy-yielding compounds of leaves, or between lion and tiger for the flesh of an antelope. Free energy of all living things must have …”— Ralph Gerard (1940) 
“Everything—the cosmos, man, culture, may be described by matter and energy. The second law of thermodynamics tells us that the cosmos as a whole is breaking down structurally and running down dynamically; matter is becoming less organized and energy more uniformly diffused. But in a tiny sector of the cosmos, namely in living material systems, the direction of the cosmic process is reversed: Life becomes a building up process that must draw upon free energy in non-living systems, capture it, and put it to work in the maintenance of vital process. All life is a struggle for free energy. Biological evolution is a movement toward greater organization, greater differentiation of structure, increased specialization of function, higher levels of integration, and greater degrees of energy concentration.”— Leslie White (1949)
“As Boltzmann (1886) put it, the struggle for existence is a struggle for free energy.”— Walter Yust (1952) 
“Man's whole struggle … practically every element in man’s developed civilization, may be interpreted either as an instinctive or conscious and deliberate attempt to replace disorder with order, in other words to consume entropy.”— Robert Lindsay (1963) 
“Power may be defined, for every society, as resulting from the need to struggle against the entropythat threatens it with disorder.”— Georges Balandier (1967) 
“Just as the constant increase of entropy is the basic law of the universe, so it is the basic law of life to be ever more highly structured and to struggle against entropy.”— Vaclav Havel (1986) 
“Conflict (and ultimately war) does not arise between human and nature; rather, the struggle is between more developed systems and something else that is necessarily less developed and that the physicists know as entropy.”— Jean-François Lyotard (1993)