This is true. However, suppose that all you knew about two plots of land was that one was bought for $1m and one was bought for $100k. Then, someone asks you which one you should develop.
Buying land isn't like betting on black. Land has a history, markets are (more or less) efficient, and buyers are usually rational. The sunken cost fallacy suggests the answer is a coin-toss, but in the real world, the correct answer would (usually) be the expensive plot.
I think this comes down to correlation versus causation.
The fact that someone (perhaps yourself) valued a property highly recently is correlated with that property having a high present value. But it does not cause it.
It is possible the million dollar purchase was a mistake, or that something has changed and it's now worth far less. Valuing a property highly may cause you to have paid a lot of money for it, and that might be a reason to assess the current value highly. But that's very, very different from valuing a properly highly because you paid a lot of money for it.
Buying land isn't like betting on black. Land has a history, markets are (more or less) efficient, and buyers are usually rational. The sunken cost fallacy suggests the answer is a coin-toss, but in the real world, the correct answer would (usually) be the expensive plot.