Can you have too few rental properties?

[Tim Pommett]

I'm a newbie, and recently attended my local DFW Real Estate Investment club this Saturday. I heard this interesting idea about a buy and hold philosophy in relation to vacancy:

Most investors don't own enough properties. In fact, your goal should be to own at least 20 properties. Even further, the most dangerous time in an investor's career is when they own about 5 properties.

Obviously the exact numbers can be argued, but I agree with the logic. Once you own 5, you are at the risk of multiple properties going vacant, which could be devastating. Once you have about 20 properties, the vacancy rate among your portfolio of investments flattens out. Basically it's the same idea as diversifying you stock portfolio.

Any thoughts on this? It was one of my bigger take aways from this last meeting, definitely stuck with me for some reason