There are two very different ways to fall into that one big bet investment" trap: The obvious one is greed, if you believe that you have found the best investm

There are two very different ways to fall into that one big bet investment" trap: The obvious one is greed, if you believe that you have found the best investment, why allocate funds to the second best. The less obvious one is all about UX: when people who don't consider wealth management their life's calling happen upon a fortune, they just want that money safely out of mind. And safely, to them, includes not causing unintended disagreements with the taxman. This requires keeping things simple enough to feel confident in being able to at least roughly understand what their professional advisors are doing. Obviously, an "all eggs in one basket" approach with a mainstream investment like a basic ETF would be the much lesser evil. But when people have a high base level of distrust in any wealth management professional this can easily blind them to the all-important difference between a regular whitehat tax advisor and a sleazy ponzi salesperson, making them the perfect mark for the latter.