Thank you for asking rather than bashing.
TL DR; Walk away, stuck in your way of thinking.
For those who care,
I'm sorry that this post is so long, but to explain anything worth explaining usually takes some time.
First, we can be clear that the type of fatigue the OP is posting about is not physical. It is not the type of fatigue that you feel after physical exertion. Rather, he is talking about a mental phenomenon.
Now, if it is possible for you (and all the other readers of this post) to conceive that the current "accepted paradigm" for mental health is just that -- a paradigm, but not an absolute truth. There is a model of the world which sees the world as having no intrinsic meaning/effect separate from the subjective superimposition upon it which occur in thought. It is called "Vedanta" and I have been studying it intensely for three years. No, you don't get a degree out of it, but it is a 'subjective science' of sorts that lays down subjective laws (as a scientist would) and encourages you to verify or disprove them by repeating the same experiments (as a scientist would), subjectively.
There's a comment above that deplores me for not wording my OP better. No doubt, I said what I said without justification. But careful analysis of his own comments would reveal that he is merely using rhetoric to lend strength to arguments, not reasoning. By posting like s/he suggests, you are just leaning on a current paradigm and gross generalisation.
Vedanta defines three aspects to the human personality:
- a physical aspect (body)
- an indiscriminate, emotional aspect (mind)
- a discriminate, rational aspect (intellect)
Accordingly the arrogation of these aspects to "I" results in the creation of the individuality and the appearance of ego. "I" is essentially unconditioned and free (absolute existence, knowledge and bliss -- the thought is similar to Descartes' "I think, therefore I am" in that there can be no experience without the presence of "I") which becomes limited, conditioned by the body (perceptions), mind (emotions) and thought (rational intellect).
It's useful to note that the "I" itself may become identified with _any_ object of consciousness, given enough repetition in thought. This _fact_ is demonstrated by the current proliferation of repetitive advertising and brand awareness. In fact, desire is defined in Vedanta as indiscriminate thought flow towards an object or being which results in mental agitation. Happiness, then, is merely the cessation of said agitation by contact with object/being.
Thus, if you limit your thoughts to yourself, the circle you are binding yourself to is very small. The causes and conditions required for your happiness are extremely specific because "this is what makes me happy" falls in a very small subset of the world. You become dependent upon this subset for your happiness, and the world, being changing, cannot always oblige. The whole range of emotion springs from this: the world cannot always cater to _ME_. This is selfishness.
If, however, you utilise the intellect to entertain higher values (I am doing this to improve my community/country/all humanity) then you have expanded your sense of "I" and the causes and conditions for your happiness fall in a larger subset of the world. Consequence: you are happier.
Children never "burn-out" (but are full of energy!) because they are not constantly thinking about themselves. In adults, there is more emphasis on "I" and "me". This burn out is caused by thoughts moving to the past ("OMG I FAILED") or the future ("I GOT TO GET THIS GOT TO GET THIS"). Vedanta recommends:
1) Plan your course of action thoroughly, considering both the past and the future
2) Dive into action, and _while acting, engage the intellect to hold the mind on the present action_, which, co-incidentally is the definition of concentration.
This post was rushed, again. But if anyone is interested in elaboration I'm always available :)