At the same time, the real issue isn't whether the son deserves the money or if he needs to have some constraints. The larger issue, in terms of family harmony, is one of communication. To my mind, secrets about money are almost never a good idea. If the son doesn't know his mother's intentions or the rationale behind them, he's in for a big and unpleasant surprise when the terms of the estate are revealed. At the very least, he's going to discover that his mother had second thoughts about him - and he's likely to resent the privileged position she conferred on his sister. My friend's mom is free to do whatever she wants with her money, but I thought it was destructive to play favorites in this clandestine kind of way, even if her intention was entirely reasonable.
There's actually a happy resolution to this story. My friend did talk to her mother about the potential consequences of her plan, and her mother took the dialogue to heart. The mother decided to be forthright with her son. She explained her concerns about his ability to handle an inheritance and the effect a windfall might have on his motivation. This served as a bit of a wake-up call for him. He started to get his financial act together by learning about investing and making some reasonable, prudent long-term plans for using the money. Open, honest communication averted a potentially disastrous rift between the brother and the sister, and dramatically improved the relationship between the mother and her son. Conversations, even difficult ones, facilitate family harmony.
If you have any wealth at all, you're going to reach a point where you have to make decisions about how you'll dispose of it when you're gone. But remember this: Even a small amount of money can have an enormous emotional impact.
There's no better time than the present to talk about your decisions with the people you care about. Tell them what you're planning to do, and more importantly, tell them why you're planning to do it. In other words, don't underestimate the power of the emotional legacy you might leave along with your financial one.