MoneyWeek article - how to invest when markets hit record highs

One of the all-time great fund managers, Peter Lynch is famous for saying, "Far more money has been lost by investors preparing for corrections or trying to anticipate corrections than has been lost in corrections themselves."
Noone can time the market and trying to ancicipate a 'drop' can be as catastrophic as taking money out during a drop. What if you were wrong?
It is more important to be prepared than it is to be right, having an investing strategy that is linked to sound planning and with a level of diversification matched to your risk tolerence removes the need to be right.
As the British philosopher, Carveth Read said, "It's better to be vaguely right than exactly wrong."

Every time markets have reached a new high, there are questions over whether it's a "good" time to invest. The only time it wouldn't be, is if you believe this is the highest it's going to be. Nobody can predict what'll happen next or time the markets to the extent that they will know when the time is right. Waiting for markets to drop is futile.

Psychologically, it can help to phase a large lump sum into the market over a period of time, which takes away some of the risk of investing the lump sum only to see markets drop shortly after. However, the stats show that it's more likely to be better to get it into the market as soon as possible.

It should always goes back to what makes most sense within the context of a financial plan. When will the money be needed, what's the reason for investing in the first place etc.

“The stock market is a device to transfer money from the impatient to the patient” said Warren Buffett. If you’re investing for the long term, timing the market is a fool’s game. However, if you have a lump sum, it does make sense to phase investments over several months, mainly to avoid haplessly investing the day before a market downturn.

It is important to consider your choice of stock market too. Recently, the US S&P 500 index has been driven by tech stocks and is now dominated by the ‘magnificent 7’ (Apple, Microsoft, Alphabet, Amazon, Tesla, Meta, & Nvidia). By investing in the S&P 500 you are taking quite a large bet that the bull run in technology will continue.

The S&P 500 is also the most expensive benchmark in the world, so perhaps it’s worth considering the MSCI World Index which invests in 23 developed markets (1,480 stocks). The World Index, excluding the US, trades on a 19% discount to the S&P 500 on forward earnings, with the FTSE 100 on a staggering 45% discount.