Perhaps it's not about the person with the most money, but being happy with what you have..?.
If you are "doing it for the money" then perhaps enough will never be enough. I invest in property because it is what interests me. I like improving the value of properties I buy because I'm good at it and I get personal satisfaction from doing so. Enough for me will be when I no longer have an interest in doing whatever or something else takes my interest more. I could develop an interest in commercial in the future and move some of my money into that, or (hopefully) take more of an interest in shares and build a better portfolio. I doubt I will ever stop investing though. Not for the money, but because I find investing enjoyable.