Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

The Joke

A child asks their father "Daddy, why do you love coffee?" The father begins a poetic, philosophical response: "When I pour in the cream, it makes the smooth, oaky taste with the sharp flavor of the coffee..." The child interrupts, offering to show him something, and the father launches into an even grander meditation: "This reaction can never never in the cosmos be undone. Entropy is irreversible." He goes on to explain that the two of them sitting together, watching the universe unfold, are sharing a moment that can never be repeated -- "one morning we make it to die, just a little bit of taste."

The final panel reveals what is actually going on. The child and an older woman (perhaps the mother or grandmother) look at the father and ask "Why does Daddy always get so weird about coffee?" The answer: "The universe started it." The joke is that a simple question about coffee preference has spiraled into an existential meditation on entropy, the arrow of time, and the irreversibility of the universe -- all because of cream mixing into coffee.

The Humor

The humor comes from the massive disproportion between the question ("why do you like coffee?") and the answer (a lecture on thermodynamic entropy and the meaning of existence). The father is not wrong -- cream mixing into coffee is indeed a textbook example of entropy in action, and the moment is technically unrepeatable -- but this is a wildly inappropriate level of cosmic significance to attach to a morning beverage. The child's bewildered reaction and the family's weary familiarity with Dad's coffee-induced philosophizing makes it clear this is a recurring event. Weinersmith is lovingly poking fun at the type of person (often a physicist or philosophy enthusiast) who cannot experience simple pleasures without turning them into meditations on the fundamental nature of reality.

References

The comic references the second law of thermodynamics, which states that entropy (disorder) in a closed system always increases. The mixing of cream into coffee is a classic textbook example of an irreversible process -- once mixed, the cream and coffee cannot spontaneously separate. This is often used to illustrate the "arrow of time" in physics.