Air and water
These elements do not share a language. Libra processes a difficulty by discussing it into a fair shape; Pisces processes it by feeling through it until it changes. Each finds the other's method slightly beside the point.
The pairing is nevertheless a gentle one. Neither sign is harsh, neither raises its voice easily, and both are unusually attentive to the atmosphere of a room. Ordinary domestic life in this combination tends to be pleasant, and pleasantness is doing more work than either realises.
Cardinal and mutable
Modality supplies the only structure available. Libra initiates and Pisces adapts, which means decisions are made on one side and absorbed on the other.
Five signs apart, the pair share no element, no modality and no ruler, so nothing about the arrangement is automatic. Libra's initiating is itself conditional, since it prefers agreement to authority, and Pisces will agree to almost anything rather than object. Two people who both want the other to decide can leave a matter unresolved for a remarkably long time.
Venus with Neptune and Jupiter
Libra is ruled by Venus. Pisces answers to Neptune in modern practice and to Jupiter in the traditional scheme. Venus idealises, Neptune dissolves the outline, and Jupiter enlarges whatever it finds.
None of those three is a realist. Between them they describe a pairing inclined to see the best version of a situation and to stay with that version past the point where it is accurate. The condition of Venus and Neptune in the two charts tells you how strong the tendency is, and Saturn contacts anywhere in the comparison are what keep it grounded.
Where it grinds
Nobody says the difficult thing. Libra softens it until it is unrecognisable and Pisces withdraws instead of stating it. Problems therefore go unnamed and get handled by hint, mood and inference, which is an unreliable way of running a household.
The second point is practicality. Neither sign has much earth in its nature, so money, admin and repairs get postponed by mutual agreement. This is the most common way the pairing gets into real trouble, and it happens without a single argument.
Why the sun signs are only a starting point
A sun-sign reading generalises across a twelfth of the population. It gives a plausible sketch of a temperament and no account whatsoever of two specific people.
Venus in both charts matters most here, since it rules one side and governs how affection and fairness are handled. Mars is worth checking too, because it decides whether anyone in the pairing is willing to be direct. The Moons then explain what each needs when things are difficult.
Questions people ask about this
Are Libra and Pisces well suited?
They are gentle with each other and rarely combative. The shared difficulty is that neither will state an objection plainly.
What is the practical risk?
Postponement. With little earth between them, money, admin and repairs slide, and the trouble arrives without any argument preceding it.
Do Venus and Neptune help or hinder?
Both incline towards the flattering version of a situation. That makes the pairing kind and also slow to notice a problem.
What should I read beyond the Suns?
Venus first, then Mars for directness and the Moons for need. A sun-sign match describes a population rather than a couple.