I'm sure you would say the same thing when the chart was at 2000 or 2008.
Chart goes higher, until it does not.
The best time to buy is not when the chart is at such an elevated point, even if it could continue to run for awhile more.
You can see in the same chart you posted, the chart went nowhere from 2000-2008
S&P500 was at 1498 on March 2000, crashed before recovering to 1500+ just prior to GFC in Oct 2007 then crashed again before finally reaching 1498 on April 2013.
All time view S&P 500 Index Chart — SPX Quote — TradingView
...13 years of Buy and Hold with nothing to show for, if one does not when to take profits and when to buy, but just holding.
...If It Hasn't Happened, It Does Not Mean It Won't.
Although as Henrik Zeberg and even David Hunter suggested, we are likely to get a Melt-Up first, but the Melt-up is already underway and getting exhausted.
...that said, all the bullishness on Wall St is falling on deaf ears on ASX. Because we do not have the moat and tech that they do. Our heavily resource weighted ASX are simply reflecting the struggling global economy of this time, which is running in disconnected fashion with the US major indices.
...as a long term follower of this thread, I am surprised you have not learnt much, if you show me the S&P500 chart. Under the hood, a lot of US stocks are doing rather poorly, its just the selected few mega techs doing well, which is why we have no market breadth.
