In general, are human beings lazy creatures? Yes or no, and please state your reasons.
Thank you,
It is calorie retention. Both work and thought require us to burn more calories. Therefore both our bodies and our brains discourage effort beyond a particular level which is individual to each person. Some people are born with either less discouragment or more motivation to overcome the discouragment.
Muscle fatigue is real, however the sensation can be exaggerated. You can feel more exhausted than you actually are. How long can you hold your breath? With practice you can extend this time, but it costs your body energy to take larger breaths or causes your body to feel more energized, which will cost you more in calories indirectly. If you are not in the practice of large breaths your capacity shrinks, to save energy. Try solving a diffult puzzle. You will feel frustration. What is that frustration for? It doesn't help you to solve anything, so it is specifically to discourage you from more mental effort.
Finally chemical stimulants are evidence that this is true. They make us feel less tired, so that we work more without feeling fatigue including mental fatigue, pains and aches. There are also natural stimulants which the body produces on its own at particular times.
There is another cause which is not just caloric. It is (I presume) an evolutionary development to cull the weak, the old, those with mental problems and those who feel unsuccessful. We call it 'Depression'. Its like having a built in enemy that can be triggered by any number of situations; and it suppresses all activity making a person seem extraordinarily lazy.