How much money toward real estate vs. stocks?

[Ian Lockwood]

Hi all! Lately I've been contemplating this question and finally figured I should toss it out to the BP community. I'm curious how everyone decides how much of their money allocated for "investing" is put toward real estate acquisitions vs. stocks/bonds. For simplicity sake let's say "stocks/bonds" represent low cost index funds (largely hands-off), with an asset allocation that makes sense for a given persons age, geared toward saving for retirement. 

I not as interested in which is better (which has been debated at length in other threads), because I think they both have their place. Let's agree that they both can have value. What I'm curious about is are people putting 100% of their "investing" funds toward real estate and forgoing any stock market investing, or splitting it 50/50, or some other percentage? Diversification is always touted as an ideal approach, right? And what is the rationale for more or less in either direction?

Using a simple real world example, the maximum 2019 Roth IRA contribution is $6,000 per year. If a couple could max this out two years in a row, they would have contributed $24,000 toward "investments." However this also means that every two years they would have enough for a down payment on an investment property. Would you say put it all toward the investment property, or go 50/50 which would mean a $24,000 down payment every four years instead? Or maybe 75% toward real estate and 25% towards stocks/bonds? How would age effect this, since getting into the stock market sooner is always better to take advantage of exponential growth and to ride-out the highs & lows?

I realize this is an over-simplification of a complex question but I'm curious how everyone approaches this. I'm sure not every BP member is 100% all-in on real estate, so those individuals must have a rule of thumb for how much of their "investment" funds go toward different types of investments - real estate, stocks, other...

I'm eager to learn how everyone approaches this. I know I have been wrestling with it for some time now. 

Coincidentally this informative @Matt Faircloth video (https://www.biggerpockets.com/renewsblog/real-estate-investing-over-stocks/) was posted today and touches on this topic, but does not get into specifics about allocating different amounts of money between real estate and stocks/bonds. Unless of course the game plan is "All In" on real estate investing, which would certainly make me rethink my approach moving forward the next few years.