This is an interesting bit of argumentation and slight of hand:

It is only after a man has got rid of all pretension, and taken refuge in mere unembellished existence, that he is able to attain that peace of mind which is the foundation of human happiness. Peace of mind! that is something

Consider the argument:

If I rid myself of X & take Y, then I’ll get Z

Z is the foundation of human happiness.

Z is wonderful.

The force of the argument is the weight it puts on Z, “peace of mind”. Peace of mind is truly a good thing. The slight of hand takes place in the logical movement from the conditions to the conclusion: Is there really any logical connection?

First, “It is only after a man has got rid of all pretension”. What is the pretension according to Schopenhauer: that the world is meaningful; that there is any providence in this world.  You can only have peace of mind if you realize that your life is meaningless.

The argument is attractive because it makes one sound rational and brave. But we need to stop at that the matter of rationality. What does rationality even mean if the universe is meaningless? Reason can’t have any “real” ground: it is simply an assertion. If the universe is irrational, how then I can assert rationality? Rationality is simply an assertion, a trick of language. How do we say a thing is “true”, if there is no meaning.

Here is the point: Schopenhauer needs rationality and reason and meaning to even begin to assert that the universe is meaningless. I recall reading in Buddhist literature years ago about the need to speak and not speak: the sound of one hand clapping. The assertions of meaningless and ultimate insubstantiality of existence mean that one must speak and then not speak of such things. While there is a remarkable difficulty in the Buddhist position, it is at least honest.

Schopenhauer’s position, I would assert, is incoherent.

What then is the psychological connection between the insistent conclusion that the world is irrational and meaningless, and that I am incoherent, with peace of mind. Wouldn’t such an assertion be anxiety producing?

Moreover, if one considers terror management theory, the assertion that fear of death requires one to raise some sort of psychological defense in order to ward off the anxiety of approaching death; then one would assert that some sort of unvarnished I’m going to die and life is meaningless position would not produce peace.

We can see that Schopenhauer then quickly moves to a position of reason and order:

Limitations always make for happiness. We are happy in proportion as our range of vision, our sphere of work, our points of contact with the world, are restricted and circumscribed.

And:

Simplicity, therefore, as far as it can be attained, and even monotony, in our manner of life, if it does not mean that we are bored, will contribute to happiness; just because, under such circumstances, life, and consequently the burden which is the essential concomitant of life, will be least felt.

What these positions reduce to, psychologically, is that avoiding circumstances which have the potential of producing anxiety helps one to feel better. Ignoring problems which cannot be resolved is an obvious means of reducing anxiety – but what this has to do with the underlying assertion that life is meaningless is difficult to understand.