tao teh ching 33

Knowing others is wisdom;
Knowing the self is enlightenment.
Mastering others requires force;
Mastering the self requires strength.

He who knows he has enough is rich.
Perseverance is the sign of will-power.
He who stays where he is endures.
To die but not to perish is to be eternally present.

Once again I give Lau in his totality:

He who knows others is clever;
He who knows himself has discernment.
He who overcomes others has force;
He who overcomes himself is strong.
He who knows contentment is rich;
He who perseveres is a man of purpose;
He who does not lose his station will endure;
He who lives out his days has had a long life.

The Ma wang tui text says much the same.

Wang Pi's commentary says:

Knowing others consists in nothing more than using intelligence which falls short of knowing oneself as this transcends intelligence (cf. ch. 16).
Conquering others consists only in using strength and this falls short of conquering oneself in which there is no-one else's strength to sap. Using intelligence on others is not nearly as good as using intelligence on oneself. Using strength on others is not as good as using one's strength on oneslef. If one's perspicacity is used to enlighten oneself, no-one else will escape it. If strength is used on oneself, no-one will usurp one's place.
One who knows contentment is not wanting in anything.
One who acts with diligence and ability will surely realise his goal.
If one examines oneself with perspicacity, acts in accord with one's own strength and does not lose one's place, one will surely endure.
Though one may die, thanks to the Tao by which one lives one is not destroyed and may thus enjoy the fulness of one's days. If the Tao continues after one's person has ceased to exist, how much more likely is it, then, that it will continue while one is still alive?

Cheng says: Although it takes intelligence to know men, how can this compare with the insight of the man who knows himself? In other words, although the man who know others is intelligent, he is ultimately only a great fool. One who conquers men, although capable and strong, cannot be compared with one who has with steadfastness conquered himeself. Lao-tze stresses steadfastness - using the soft to overcome the hard - and hence says, 'directing the breath by the heart/mind is called steadfastness'. How this is in contrast with 'the strong will come to an untimely end'!
One who knows sufficiency is not greedy, and one who is not greedy feels wealthy with what he has. Certainly 'One who pursues his aim with steadfastness has will-power': how can one attain to non-action and freedom from desire without a firm will?.
'One who dies yet still remains' refers to someone whose Tao has not perished though they, themselves, have gone. This is longevity: 'though the body ceases to be, he is not destroyed.'.

This chapter deals with several things, all of them pointing back at the conceived 'self' and 'owner of the perceptual situation' as not quite adequate to what is actually going on.
As long as we are attached to the solid 'reality' of 'things', no matter how intelligent one seems to oneself or others, this is nothing but skill in interpreting and manipulating one's own projections, or - in a word - 'ignorance'.
Relatively speaking, of course, things are - more or less - things... what they seem to be... Day is day, night is night, a cat is not a guitar... The problem arises, not in the fact of the catness of the cat and the guitarness of the guitar, but in our attachment to the idea that 'cat' or 'guitar', 'day' or 'night' are somehow monolithically what they are - that cat is somehow permanently and independently cat beyond the various elements that are its ever-changing form, feelings, perceptions, reactions and conscious awareness... that we are us beyond ours... that there is some enduring essence that is an ultimate us over and above oft ignored or rejected embeddedness in the energy-field that is the continuum of becoming.
As long as we do not actually know what we and our world are and how they function, any 'knowledge' as regards a world we imagine we perceive, to use John Lynn's expression, falls short of reality... it is not reality... it is nothing but a focus-pull being taken for the whole.
Consciousness is strange stuff: it is aware only of whatever it fixes its sights on, and this only ever in the way it fixes its sights.
A mosquito, for example, is not in the slightest bit interested in or even vaguely turned on by the naked body of your lover. All that interests her about this presence is the 'fact' that here at last is nourishment for her eggs. Everything in the realm of discursive awareness is like this - it is impermanent, utterly dependent on everything else for survival, embedded in an ever increasingly vast whole and yet itself made up of ever diminishing 'parts' and 'instants', all of this circumscribed by ever-fluctuating 'intention'...
The Tao is - in a certain sense - the state beyond all this coming-and-going... It is the vastness of which the comings-and-goings of all description are merely the present point-instant of manifestation.
To dwell with this and yet not be attached to it - not to get swept off on the endless sea of becoming or get stuck in and disappear into a totally imaginary 'void' - requires strength... steadfastness... This is the discipline of realising you have enough - that the mere fact of your continued presence here for even an instant is the gift of the entire universe which supports you.
One who stays with the source yet embraces the unfoldment cannot be shaken and thus endures. The mere fact of being this, that or the next thing is of no special interest to them - the whole thing, in both its 'on' and its 'off' position is what's so incredible.