The Motley Fool reported this week that Berkshire Hathaway has increased its stake in Lennar, the big homebuilder. On the surface this looks like a gift to everyday investors: the smartest money in the room is buying a beaten-down stock, so shouldn't you saddle up alongside it?

I'd slow down before copying the trade, and I'll explain why. But the case for why Berkshire might like it is real, so let's start there.

Lennar is one of the largest homebuilders in the country, and homebuilders as a group have been dragged down by high mortgage rates and soft demand. When a solid business trades at a discount to what it's worth, that's the kind of thing Berkshire has built a six-decade record on. The Fool's piece makes the point that this fits Berkshire's broader style, and it does. Buffett and his team have always liked businesses with real assets, steady demand, and prices that already assume bad news. Housing checks those boxes eventually, because people always need somewhere to live.

Now the caveats, and they matter more than the headline.

First, size. Berkshire's portfolio runs well over $300 billion. A position in Lennar, even a growing one, could be a rounding error for Berkshire and still be a meaningful bet for you. When a company that big buys a stock, it tells you somebody there saw value. It does not tell you how much conviction is behind it. If I gave a waiter a 30 percent tip on a $12 lunch, that's a strong signal about the service. If a billionaire did the same, you'd learn nothing.

Second, you don't know the whole picture. Berkshire also holds cash that dwarfs most positions, hedges you'll never see, and a time horizon that comfortably outlives any of us. You're copying one card from a hand you can't look at.

Third, and this is the part I'd underline: by the time a 13F filing shows a purchase, the trade happened months ago. You're not buying where Berkshire bought. You're buying after the stock has already been bid up by everyone else who read the same filing. I've watched this pattern play out for years. The followers usually pay more than the leader, and they're the first to sell when the stock dips, because they never had a reason to own it in the first place.

None of this means Lennar is a bad investment. Homebuilding is cyclical, and buying good cyclical businesses when sentiment is ugly has worked for a very long time. If you understand the industry, you've looked at Lennar's land position, its margins, and its balance sheet, and you believe in a housing recovery on a timeline you're willing to sit through, that's a legitimate thesis. Lennar might even deserve a spot in the speculative corner of a portfolio, sized so that being wrong doesn't wreck your year.

But buying it because Berkshire did isn't a thesis. It's delegation to someone who doesn't know you exist. The question that matters is the one Berkshire itself would ask: what is this business worth, and what are you paying for it? Answer that yourself, with numbers, before you answer the question in the headline.

For most people the boring answer still wins. A broad index fund doesn't require you to guess which homebuilder recovers first, and it already owns a slice of Lennar's sector along with several thousand other companies. If Berkshire's move tempts you, let it tempt you into doing research, not into doing what you're told.

As always, I'm sharing perspective here, not professional financial advice. I've been wrong before and I'll be wrong again, just hopefully not in the same paragraph.