Because I move your watch slows down.
Or as Alan Lightman said on a PBS documentary about Einstein, "different clocks in motion relative to each other tick at different rates."
We've been lead to believe this...it just makes sense, amirite???
Ed McQuarrie talks the REAL History of Stocks and Bond performance.
https://www.morningstar.com/funds/most-stunning-fact-about-vanguards-etf-flows-2
This article shows people are pulling money out of mutual funds and putting it into index funds an example is VOO. Also Vanguard Primecap and Core fund opened the fund due to them both because of money being pulled out. INDEX ETF's way to go tax efficient and low expenses