Umm, no. That's not it at all. In fact, that doesn't even fall 100 yards within what actually happens.
With Eminent Domain, the government has to pay you just compensation. This means that for the government to take something from you, they have to pay only what it is worth.
But worth is a very subjective value. For example, property values. Property values swing based on the market at the time, ontop of value differences from one appraiser to the next.
One appraiser could lowball a number, while another could overshoot. The only way to really find out what it is worth is to actually put it on the market and see what it goes for. And even that changes from buyer to buyer.
So the government grabs lowball appraisers and gives you the lowball amount. You could fight in court how much the house is worth, but then you have to consider court and lawyer fees, which might then over take what you would be losing.
Add ontop of that, the idea that sentimental value means nothing. You could have had a family farm for many generations and given birth to 10 presidents in your guest room alone, if the government wants your land, they'll give you what they deem proper.
But the worst thing of all... If the government wants your land, they'll have it.