"Overbought" does not mean "about to fall"
The Relative Strength Index compares the size of recent gains to recent losses over N periods, scaled from 0 to 100. Above 70 is conventionally "overbought," below 30 "oversold."
Those two words have probably cost retail traders more money than any other pair in technical analysis, because they sound like predictions and are not.
What RSI actually measures
The ratio of up-moves to down-moves over the lookback period. Nothing else.
RSI at 80 means: over the last 14 periods, gains have massively outweighed losses. That is a description of the recent past. It is a statement about momentum being strong, not about price being expensive or a reversal being due.
Read literally, "overbought" means *"this has gone up a lot lately."* In a strong trend, that is the definition of a strong trend.
Why fading it fails
In a genuine trend, RSI can sit above 70 for weeks. Every day it stays there, someone shorts it because it is "extreme," and every day they are wrong.
The instrument does not care about the reading. There is no mechanism by which a calculated ratio exhausts buyers.