When the need for illusion is deep

Saul Bellow:

A great deal of intelligence can be invested in ignorance when the need for illusion is deep.

Objectively I would wager that is true but I suspect it shines a light on an underlying paradox. Reality serves up many unexpected, and not infrequently, undesirable changes. Some of those changes we can resist or mitigate and others we cannot. Our challenge is to know the difference between the two. That challenge is famously reflected in Reinhold Niebuhr's Serenity Prayer.

God, grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And wisdom to know the difference.

Resisting usually entails sustained effort over long periods of time, frequently in circumstances where objective data supports that it is a lost cause. We sustain our activity by creating the illusion that we will win out despite what our objective senses are telling us. Some cultures are more prone to this than others. In the US, there is a deep love and admiration for the lone individualist who bucks the trends, stays the course and triumphs against the odds.

In those circumstances, we celebrate the fact that "a great deal of intelligence can be invested in ignorance when the need for illusion is deep." But it doesn't always turn out that way and then we are puzzled that so much intelligence was invested in so clearly a stupid idea for so long. It calls to mind Shakespeare's words in Hamlet Act III, Scene 1:

To sleep: perchance to dream: ah, there's the rub;
For in that sleep of death what dreams may come
When we have shuffled off this mortal call,
Must give us pause. There's the respect
That makes calamity of so long life;
For who would bear the whips and scorn of time,
The oppressor's wrong, the proud man's confumely,
The pangs of disprized love, the law's delay,
The insolence of office, and the spurns
That patient merit of the unworthy takes,
When he himself might his quietus make
With a bare bodlcin? Who would fardels bear,
To grunt and sweat under a weary life,
But that the dread of something after death
The undiscover'd country from whose bourn
No traveller returns, puzzles the will,
And makes us rather bear those ills we have
Than fly to others that we know not of?
Thus conscience does make cowards of us all;
And thus the native hue of resolution
Is sicklied o'er with the pale ease of thought,
And enterprises of great pith and moment
With this regard their currents turn awry,
And lose the name of actions.

How do we know when it is appropriate to invest a great deal of intelligence in ignorance when the need for illusion is deep?