A write-down is a book (non-cash) entry to bring a previously overvalued asset to the current value. The write-down results in one-time non-operating loss (which btw results in income tax savings). It’s bad on the balance sheet and also bad for earnings per share. If the value of the asset continues to decline, then it’ll have to written-down again.

The manner in which companies and industries come up with current value is highly subjective. Ideally, the value of the land should be what is would sell for today. Financial Accounting Standard Board rules determine when a write-down needs to (or can) be booked.

If a public company’s stock went down a lot, they have the incentive to write-down as much as possible because they figure that the write-downs would not lower share price any more that it’s already been by other factors. In the future, they get to book higher profits from selling the lower basis asset, thus influencing share price on the up side.

A private company would want to write-down everything it can in order to defer taxes.