As the title of the poem suggests, the advice W. B. Yeats is giving out to someone already in a relationship or to would-be lover in "Never Give All the Heart" is to hold back in love. Written as a sonnet (a poem in 14 lines), the poem follows a rhyme scheme somewhat diverging from the Shakespearean form (A-A, B-B, C-C, D-D, E-E, A-A, and F-F, where a normal Shakespearean sonnet follows a pattern of A-B-A-B, C-D-C-D, E-F-E-F, and G-G).

The choice of form is apt, since a sonnet is often constructed as a poem of love addressed to a muse or beloved. The poem’s tone is borrowed from the courtly English sonnet of Wyatt, with the speaker often treating love as a game or a hunt. While in its original Italian form, the sonnet largely dwelt on an idealistic love away from the trappings of lust, in its English version the sonnet can sometimes be more carnal and cynical. Likewise, the poet’s initial tone here is skeptical of love in general and women in particular. Instead of love as a deep, fulfilling emotion, he positions it more as a contest, where the lover should fight to retain the upper hand:

Never give all the heart, for love
Will hardly seem worth thinking of
To passionate women if it seem
Certain. (lines 1–4)

In these lines, the poet is stating that “passionate” or virile and beautiful women will tire of love when they can take it for granted. What keeps them hooked instead is the thrill of uncertainty and the drama of the chase. Therefore, the lover must act aloof and unpredictable around them. Furthermore, everlasting love may also induce boredom in women, because everything that is delightful on this earth is fleeting and momentary. If the lover shows constant, unrelenting passion, the beloved will only find it tiresome:

For everything that’s lovely is
But a brief, dreamy, kind delight. (lines 6–7)

What’s more, if love is a game, the lover or the player must be at his sharpest while playing it in order to win. However, absolute, consuming love doesn’t make you sharp, the poet contends. Love “blinds” you—makes you sappy and weak—therefore making you a terrible player. Being completely in love thus is actually antithetical to the game of love. Thus the poet distinguishes between Love with a capital "L" and love as a game of courtship and lust:

And who could play it well enough
If deaf and dumb and blind with love? (lines 11–12)

But the last few lines of the poem somehow mitigate the bitterness. At first the poem seems like calculating, cynical advice from a man practiced at seduction; however, the last couplet shows the poem to be what is really is: a lover’s lament. This change in tone, or reversal, is also well in keeping with the conventions of the sonnet form in English, where a “volta” or a twirl often occurs before the final couplet.

Ironically, the volta reveals, the poet has not followed his own advice. Instead, he has gambled away everything in love, given all his heart and lost, which is why he has composed this warning note for future lovers. The poet is also rejecting the common belief that “It is better to have loved and lost than not to have loved at all.” Sometimes it is better not to have loved, he says, especially when the wages of love are self-annihilation:

He that made this knows all the cost,
For he gave all his heart and lost. (lines 13–14)

Yet the irony is that the poet did gain something very worthwhile from his consuming passion: this beautiful poem. He has memorialized his love forever in art, which brings us to a famous statement made by Yeats's real-life muse, the one to whom he gave all his heart and lost: "The world should thank me for not marrying you.” Had Yeats gone on to marry her, she seems to be asking, how would he have created perfect poems filled with longing?

The "she" in question is Maud Gonne, a famous, charismatic actress and activist of her day and Yeats's longtime muse. Although it is not necessary to use a writer’s biography to explain a text, exception can be made in the case of Yeats, especially when it comes to his love poems. Yeats himself alluded to or addressed Gonne in several of his poems. He remained madly in love with her much of his adult life, proposing marriage to her more than a few times, an offer she always spurned. Though Gonne was a great friend of Yeats’s, she accepted him as a romantic partner only very briefly.

“Never Give All the Heart” can be read in the context of Yeats’s unrequited love for Gonne. Inspired by his one-sided passion, Yeats wrote more such poems about the futility of love, including the marvelously-titled “He Wishes his Beloved were Dead!”