no two nights will teach what bliss is

in precisely the same way,

with precisely the same kisses.

From the poem “Nothing Twice” by Wislawa Szymborska

She is saying that no two events, however much alike they are, are the same. In the context of the rest of the poem, she seems to be saying that life is without rules or order but love makes that fact debatable or doubtful.

Hope this helps!

Added Notes:

I am not sure that I can summarize the poem for you, I have read up on Wislawa Szymborska, read some comments and reviews about her work and I think that those will help you to understand the poem.

My own opinion on this poem is that, even though it is listed in the “100 Best Love Poems Every Written,” I don’t think is in any way a traditional love poem. I think she is saying that we arrive on this earth unprepared for life and never really learn how to handle what life throws at us. Often we aren’t given second chances to learn life’s lessons (see stanza 2), Love is an illusion and we don’t ever know if it was real, or if our loved one was throwing roses or rocks. (a sample of the humor she was famous for in her serious poems). She is comparing love to time. Today is always tomorrow. Nothing stays the same. We use love to try and give us something to hang on to, but there is no order or rules to love or to life, so whether or not the love is real is a point we cannot be sure of.

Szymborska often uses ordinary speech and proverbs but gives them a fresh and arresting meaning. Look for instances of that is is poem. The simplicity of her poetry defies the theorizing of scholars while unerringly zeroing in on the taste contemporary readers. She uses a language of compassion for those who have been wronged, of delight at the beauty of human life with its keen beauty, illogicality and tragedy. It is a language of well-considered judgments and muffled emotions, a language of lyricism controlled by a cold, fresh intellect, a language subjected to intellectual rigor that does not rule out sensitivity to the everyday attractions of existence. It is a language that generally remains faithful to colloquial speech while subtly widening its lexical resources. It is a language of paradox, apparently simple but in fact refined and idiosyncratic.

She explored human isolation and celebrated poetic creation. Szymborska, who often emphasizes the uniqueness of the individual, has been called an ironic moralist. Her verse is deceptively simple; her language colloquial, precise, and contained; and her tone detached and dryly sardonic.

I am not sure that I can summarize the poem for you, I have read up on Wislawa Szymborska, read some comments and reviews about her work and I think that those will help you to understand the poem.

Szymborska often uses ordinary speech and proverbs but gives them a fresh and arresting meaning. Look for instances of that is is poem. The simplicity of her poetry defies the theorizing of scholars while unerringly zeroing in on the taste contemporary readers. She uses a language of compassion for those who have been wronged, of delight at the beauty of human life with its keen beauty, illogicality and tragedy. It is a language of well-considered judgments and muffled emotions, a language of lyricism controlled by a cold, fresh intellect, a language subjected to intellectual rigor that does not rule out sensitivity to the everyday attractions of existence. It is a language that generally remains faithful to colloquial speech while subtly widening its lexical resources. It is a language of paradox, apparently simple but in fact refined and idiosyncratic.

She explored human isolation and celebrated poetic creation. Szymborska, who often emphasizes the uniqueness of the individual, has been called an ironic moralist. Her verse is deceptively simple; her language colloquial, precise, and contained; and her tone detached and dryly sardonic.

Szymborska was cited by the Swedish Academy for “poetry that with ironic precision allows the historical and biological context to come to light in fragments of human reality.”

Her poetry, described by Los Angeles Times critic Dean E. Murphy, is “seductively simple verse . . . [which has] captured the wit and wisdom of everyday life” in Poland during much of the twentieth century.

Explaining Szymborska’s work, translator Stanislaw Baranczak noted in New York Times Book Review: “The typical lyrical situation on which a Szymborska poem is founded is the confrontation between the directly stated or implied opinion on an issue and the question that raises doubt about its validity. The opinion not only reflects some widely shared belief or is representative of some widespread mind-set,” Baranczak added, “but also, as a rule, has a certain doctrinaire ring to it: the philosophy behind it is usually speculative, anti-empirical, prone to hasty generalizations, collectivist, dogmatic and intolerant.”

Many commentators have remarked on the deceptively simple quality of Syzmborska’s work. In simple language, she speaks of ordinary things, only to reveal extraordinary truths. In a Publishers Weekly article about the poet, Joanna Trzeciak praised “the wit and clarity of Szymborska’s turns of phrase. Under her pen, simple language becomes striking. Ever the gentle subversive, she stubbornly refuses to see anything in the world as ordinary. The result is a poetry of elegance and irony, full of surprising turns.” And Denise Wiloch, a contributor to Contemporary Women Poets, pointed out that “the seemingly casual musings she captures in her poems are deceptive and full of irony. Her work reverberates long after it is read.”

Syzmborska “knows philosophy, literature, and history, but mostly she knows common human experience,” concludes Booklist writer Ray Olson. “Her work is ultimately wisdom literature, written in a first person that expresses a universal humanity that American poets—lockstep individualists all—haven’t dared essay since early in this century. She is like Brecht without hatred, Sandburg without socialist posturing, Dickinson without hermetism, Whitman without illusory optimism: a great poet.”

Much of this came from:

http://www.poetryfoundation.org/archive/poet.html?id=6744