There is a school of though that says our fundamental assumptions cannot consciously be chosen - or, more accurately, that if they are thus chosen then they will be feeble. The idea is that only those fundamental beliefs which we have without choice are genuinely motivating.
Robert Frost indignantly denounced college teaching that 'frisks Freshmen of their principles'. At Bread Loaf in 1925 he declared that a boy with all his beliefs drawn out of him is in no condition to learn. Or even to live. Everybody needs some beliefs as unquestionable as the axioms of geometry*. No postulates deliberately adopted could ever have the force. We had to have unarguable, undemonstrable, unmistakeable axioms, just three or four. And if we didn't abuse our minds we should surely have them. One such is genuineness is better than pretense. Another is that meanness is intolerable in oneself. And another is that death is better than being untrustworthy.
From A Swinger of Birches: a portrait of Robert Frost, by Sidney Cox (1957)
There is something valid in this argument, that requires response, because our fundamental assumptions are not arbitrary.
We surely cannot just stick a pin in a list and choose anything that comes-up as our baseline beliefs, and then expect to be motivated strongly enough to resist being derailed by the many temptations of life and infirmities of our own nature.
On the other hand, it seems obvious that - on the one hand - peoples fundamental assumptions are being inculcated-into-them by deliberate and socio-political propaganda, in ways that harm the people. So, if we just accept our assumptions as something 'given', we are in fact merely blinding ourselves to our own exploitative psychological enslavement.
Furthermore; modern motivations are actually very feeble, by comparison with the past; as can be seen by the collapse of personal courage and individuality of character - which has been very obvious and evident over recent decades. The docility, homogeneity, and automatic-obedience of Western Man is now astonishing to behold; when compared with the middle twentieth century.
So, it seems that there is no valuable alternative but to become aware of our own deepest values, assumptions, metaphysical beliefs; and to evaluate them; and then to choose between possibilities.
It is this choosing upon which all depends: because what we choose must not only be something we regard as right, true, correct; but it must also be something that provides us with a strong motivation - such that we can avoid being deflected off-course by the first problem, the first contrary expediency, we encounter...
So that we may have the courage of our convictions... Because - without courage, convictions are worthless.
People often talk as if 'will power', determination is the answer; but the strength of will-power itself derives from fundamental convictions. It is our assumptions that provide the power of will. So our will cannot overcome feeble and false assumptions. Again we are returned to the need to choose assumptions; but to choose the right assumptions.
Choosing our assumptions is (and should be) more like a quest, or a path of discovery; than it is like an arbitrary coin-flip.
It is a matter of finding our most fundamental values. We each need to find-out what things we most value, deep down, through time.
These profound values may be very different from, may indeed oppose or contradict, the values we have expressed, or implemented in previous living. Our fundamental values may be a kind of secret knowing: and, at first, secret even from our conscious-selves.
It may also be the case that these fundamental values turn out to be inconsistent among themselves, that they clash - and therefore tend to cancel-out: this may be another cause of feeble motivation and cowardice of conviction.
So the choosing of deep assumptions is also, potentially, a choosing-between.
What is the it that does the exploring, questing, discovering, choosing? That's another matter - I am talking about the real self or true self - which is also the divine self.
Only when it is the divine self who is doing the choosing can we expect a Good outcome.
If, instead, the above process was merely done by our 'personality self', that 'self' constructed by societal inculcation, a mere selfish-self, and pleasure-seeking self, or any other kind of evil-motivated self... Then clearly the end result is going to be bad (i.e. bad in a Christian sense).
It would then merely be a choice made by that which is propagandized, passive, controlled... Thus no real 'choice' at all...
Therefore, as always, there are (at least) two changes that must be made, two processes that must simultaneously be implemented.
...This is nearly always true. When only one obstacle is before us, when only one kind of change is needed for our betterment; it will usually be overcome sooner or later, spontaneously, without need for profound change.
What separates us from awakening, from betterment, from initiation of a positive transformative process; is the requirement for (at least) two simultaneous efforts: in this case 1. the need to find and work-with our real/ divine self, in 2. the project searching-for and choosing our fundamental assumptions.
In conclusion: Yes! fundamental assumptions really can be known, evaluated, and chosen; but for this to be valuable and effective entails that we discover something about our deepest values, and also that this 'discovery' is accomplished by that which is divine within us.
*Note. The fact that there is more-than-one axiomatic system of geometry, more than one set of postulates - and that the best choice between axioms depends on the function to which the geometry is being-put - undercuts Frosts analogy in an ultimate sense; although it still retains rhetorical validity.