A candle's body gets all the attention because it is the biggest shape on the screen, but the wick is the part that tells you what was rejected. Nasdaq rallies through the morning, and on one bar it pushes to 19,180, then sells all the way back to close at 19,110, leaving a wick more than three times the size of the body above it. The body says the bar closed slightly up. The wick says buyers tried for another 70 points and every one of them got sold into. That is the more important sentence, and most traders never read it.
Wicks are a record of price the market visited and then rejected. Learn to read their length, their side and how often they repeat, and you get a second layer of information sitting on top of every candle pattern you already know.
Length shows how hard the rejection was
A wick that is a small fraction of the candle's total range is unremarkable, ordinary noise from the bar testing slightly beyond its close. A wick that is two or three times the size of the body is a different order of event: real buying or selling pressure entered at that extreme and was firmly overwhelmed. On EURUSD, a wick that reaches 15 pips beyond a close that only moved 4 pips on the day is worth marking on the chart, because a level that produces a wick that size once tends to matter again.
Side shows which side got punished
Upper wicks show sellers winning the argument at the top of the bar's range; lower wicks show buyers winning it at the bottom. A trend made up mostly of candles with small upper wicks and almost no lower wicks is telling you sellers barely get a foothold, which is a healthy uptrend. The moment lower wicks start appearing with any regularity inside that same uptrend, buyers are starting to meet resistance on dips, an early tell worth watching even before any reversal candle forms.
One wick is an event, many wicks are a pattern
A single long wick at a level is interesting. Three or four long wicks clustering at the same price over several sessions is a level the market keeps testing and failing to clear, which is a far more reliable signal than any one of the individual candles. Gold repeatedly wicking up to 2,420 and closing back under it across four separate days is a stronger resistance case than a textbook shooting star that only shows up once. Traders who mark levels only from closes are throwing away this information; the wicks are often where the real fight happened.
Reading wicks inside a trend, not just at reversals
Wicks are not only reversal tools. Inside a strong trend, small consistent wicks against the trend direction show healthy absorption, dips being bought without much fuss in an uptrend, rallies being sold without much fuss in a downtrend. A sudden change in that pattern, wicks growing longer and more frequent against the trend, often shows up several candles before the trend actually breaks, which gives an attentive trader an early warning that costs nothing to watch for.