Am I doing RE investing wrong? (or not as efficiently)

[Joe B.]

I currently own 1 SFH. Bought it in 2018, house hacked it, and now live with my girlfriend. That house now gives $700 month in positive cash flow. 4 years later however, I am still at that one unit. Now, I am ready to jump on a multifamily that comes across my eye. I would love a 4-plex, however if the numbers work, I will be open to something smaller.

I study everything RE related religiously, whether podcasts, books and much more. Every now and then I will come across a podcast in which a person owns 50+ units just in their mid 20s which is impressive! My question is, what strategy are they using to make that achievable? With a generous w2 job and numerous side hustles, I still only own 1. Am I missing something here?