Indicators summarise rather than predict. Knowing what they summarise prevents misreading.
Most indicators placed on a chart take prices that already happened and run them through a formula. They add no new information; they organise what has occurred into something easier to read. Saying an indicator gives a signal is therefore imprecise. It shows, in one number, what recent movement has been like.
Some indicators express the balance of recent rises and falls as a value between zero and one hundred. A high value means it rose a lot recently and a low value means it fell a lot. These are commonly called overbought and oversold, and those names invite the misreading that a reversal is due. In a strong trend, the value can stay high for a long time.
Dominance expresses one asset's share of the whole market. A rise can mean that asset went up, or that everything else fell further. Ratio indicators move through both numerator and denominator, so deciding the cause from one number alone is error-prone.
Indicators expressing fear and greed as a number combine several inputs such as volatility, volume and search interest. What is mixed in, and at what weight, differs by whoever builds it. The same-named indicator therefore carries different values from different sources, and reading changes within one source misleads less than reading the absolute number.
Load enough indicators and at any moment something says buy and something says sell. You then end up selecting whichever agrees with you, which does not aid judgement so much as support a decision already made. Knowing what an indicator computes matters more than how many you use.
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