It seems it's about pride:

Psalms 131:1 HCSB
Lord, my heart is not proud;
my eyes are not haughty.
I do not get involved with things
too great or too difficult for me.

Psalms 131:1 NASB
O LORD, my heart is not proud,
nor my eyes haughty;
Nor do I involve myself in great matters,
Or in things too difficult for me.

Psalms 131:1 MSG
GOD, I'm not trying to rule the roost,
I don't want to be king of the mountain.
I haven't meddled where I have no business
or fantasized grandiose plans.

Gill:
neither do I exercise myself in great matters; or, "walk" (m) in them; these were not the subject of his employment and conversation; he did many great things, in killing the lion and the bear that came into his father's flock; in slaying Goliath with a sling and stone only; in leading out the armies of Israel, and slaying his ten thousands; and he exercised himself in the great things of the law, which he was careful to observe, and studied the great things of the Gospel, which he had the highest esteem of, and desired to understand; but he did not seek human greatness, or the great things of this world, for himself; he had no ambitious views, or was desirous of the kingdom he was anointed to, before the proper time; see 1Sa_18:18;

or in things too high for me: or "too wonderful" (n); see Job_42:3. He contemplated the wonderful make and frame of his body, the texture, symmetry, and use of each of its parts; he observed the wonderful providences of God towards him ever since he had a being; and particularly he took notice of the wonderful love of God to him, and remembered and talked of, and declared, the wonderful works of grace and redemption; but not things above his capacity, out of his reach, and which are secret, or not clearly revealed: and such things we should be content to be ignorant of, or not to have adequate ideas of, or be capable of accounting for;

i dont disagree wtih you about those first two lines... but the next few... I still feel like it's discussing adventure... our dreams, desires, open doors, ambition etc...

"or fantasized grandiose plans."

?

Well that's The Message.

I suppose there is a wide scope and motives for dreams desires ambition etc.

I'm thinking i've narrowed it down this way:

my heart is not lifted up - I keep myself humble
my eyes are not raised too high - my eyes are not haugty (scornfully or condescendingly proud) - I do not look down on others

i am not concerned with things too big for me. (maybe, I dream big but not too big, about myself. ambition vs. fame or buidling your own kingdom. Being a good minister vs. famous blogger. )

i keep my dreams in check
i calm myself by detaching myself from that to which i am strongly habituated or devoted


Hope in the Lord
NOW! and always!


Humility in light of the Lord,
Hope in the Lord


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so there is humility... i think you're right the more i look at it...
but still sorting through it... i'm wanting to teach on this but having difficulty grasping it... teaching on it when failing to grasp it isn't probably the BEST idea... hopefully i get somewhere.