It depends what your goal is, and how much risk or volatility you can stomach along the way.

Many moons ago we were planning to refinance the house at a much lower interest rate. I had been reading TMF for a while, and after running numbers I said to friend wife "We can refi the balance and have a lower payment, or we can take $20,000 cash out and invest it and have the same payment as we have now." (This was way back when they didn't penalize you if you did a cash-back mortgage.)

She thought it out for a few seconds and said "We aren't having any trouble making our current payment, So if you think investing is good, let's do that. And if we lose the entire $20,000, we are no worse off that when we got married with our net worth was however much gas was in the car."

Years later, we retired at age 58.

I think that is the idea, you assess how much loss you can take along the way.
Twice we had two -50% losses.

My Dad took me aside and told me that the worst mistake he had ever done was panic on Black Monday 1987 and sold everything because they "couldn't afford" to lose their investments.

Once you get to a certain stage of your life, and to a certain age, you mostly are investing not for yourself but for your kids & heirs. That changes the emotional impact of volatility and drawdowns on you.