vain

If you are describing a person who is "too full of themselves" or "too obsessed with their own image", they are vain. It is premature adulation.

If you are describing an action or an attempt that fails because it is inadequate and "too little, too late," it too is vain. (As in vain attempt).

So the first use of vain is about being too full , the second is about being empty . The first use is about jumping to a conclusion, the second is about concluding too late.

God help me, I love this kind of stuff

Vain (?), a. [Compar. Vainer (?); superl. Vainest.] [F. vain, L. vanus empty, void, vain. Cf. Vanish, Vanity, Vaunt to boast.]

1.

Having no real substance, value, or importance; empty; void; worthless; unsatisfying.

Shak.

Every man walketh in a vain show. Ps. xxxix. 6.

Let no man deceive you with vain words. Eph. v. 6.

Vain pomp, and glory of this world, I hate ye! Shak.

Vain visdom all, and false philosophy. Milton.

2.

Destitute of forge or efficacy; effecting no purpose; fruitless; ineffectual; as, vain toil; a vain attempt.

Bring no more vain oblations. Isa. i. 13.

Vain is the force of man To crush the pillars which the pile sustain. Dryden.

3.

Proud of petty things, or of trifling attainments; having a high opinion of one's own accomplishments with slight reason; conceited; puffed up; inflated.

But wilt thou know, O vain man, that faith apart from works is barren? James ii. 20 (Rev. Ver.).

The minstrels played on every side, Vain of their art. Dryden.

4.

Showy; ostentatious.

Load some vain church with old theatric state. Pope.

Syn. -- Empty; worthless; fruitless; ineffectual; idle; unreal; shadowy; showy; ostentatious; light; inconstant; deceitful; delusive; unimportant; trifling.

© Webster 1913.

Vain, n.

Vanity; emptiness; -- now used only in the phrase in vain.

For vain. See In vain. [Obs.] Shak. -- In vain, to no purpose; without effect; ineffectually. " In vain doth valor bleed." Milton. " In vain they do worship me." Matt. xv. 9. -- To take the name of God in vain, to use the name of God with levity or profaneness.

© Webster 1913.