Three cups, and one being held out
A figure sits under a tree with arms folded, looking down at three cups on the ground. A hand comes out of a small cloud holding a fourth. The figure is not looking at it. Nothing in the scene is wrong: the setting is pleasant, the cups are intact, the offer is being made politely.
That is the discomfort the card is built on. There is no injury in the picture to explain the mood. The tradition reads it as dissatisfaction with circumstances that are perfectly adequate, which is a more honest description of most low periods than grief is, and a harder one to argue with.
Upright and reversed
Upright, the reading is an offer refused out of a flatness you cannot account for. Boredom, apathy and reflection are the keywords, and reflection is included deliberately. Withdrawal is not always a fault. Someone who has just come out of a demanding stretch may need the folded arms, and the card allows for that.
Reversed, the readings run in opposite directions and both are standard. One is coming out of it: the fourth cup gets noticed, interest returns, the offer is looked at. The other is sinking further in, the withdrawal deepening into something more settled. Nothing in the card decides between them. The rest of the spread and the querent's own account of how long this has been going on are what a reader actually has to work with.
Four in the suit of water
Fours across the suits describe something held in a settled state. In Pentacles that is money kept, in Swords it is rest taken, in Wands it is a pause enjoyed. Cups is the suit of feeling, relationship and what matters to you, so a four here is a mood being held rather than an object.
That is why the card reads as stuck rather than as unhappy. A held mood is stable, which is exactly the problem with it. There is no astrological attribution for this card in the system most decks use, since those correspondences attach to the majors and the court, so the reading rests entirely on the number and the element of water.
What it asks
A reading is a prompt for thinking, not a source of information about what happens next, and this card puts a two part question that is worth taking in order. First, what is currently being offered that you are not looking at. Second, and only afterwards, whether the flatness is telling you something true about the offer.
People collapse those two into one and usually get it wrong. Sometimes the fourth cup is genuinely not worth taking, and the tradition does not insist otherwise. Sometimes the flatness is the whole of it and the offer is fine. The card does not know which, and it should not be read as an instruction to accept anything. If the mood has lasted long enough to worry you, that is a matter for a doctor rather than a deck.
Questions people ask about this
What does the Four of Cups mean?
An offer refused out of a flatness the querent cannot explain. Boredom, apathy and reflection sit around it, and the card is careful not to say whether the offer or the mood is the real issue.
Is the Four of Cups about depression?
The tradition describes a low, unexplained flatness, which overlaps with how people describe low mood. It is not a diagnosis and should not be used as one. A mood that has lasted is a question for a doctor.
What is the fourth cup?
An offer being made that the figure in the image is not looking at. Readers usually take it as something available now, though the tradition does not claim the offer is necessarily worth accepting.
What does the Four of Cups reversed mean?
Either coming out of the flatness and noticing what is on offer, or sinking further into it. Both are standard and the card gives no way to choose, so the surrounding cards and the querent's account decide.
What element is the Four of Cups?
Water, the element of the Cups suit, which covers feeling, relationship and what matters to you. Like the other numbered minors it carries no planet or sign of its own.
How does it compare with the Four of Swords?
Both are fours and both describe a stop, but the Swords card is rest that is needed and often not chosen, while the Cups card is a mood being held while life carries on around it.