Nick Roweそう書いている(原題は「Cash as the real real option -- to do anything」)。以下にかいつまんで紹介する。

Option theory was originally about financial assets called options.
Then people noticed that this could also be a useful way to think about investment decisions in real assets (bricks and mortar etc.), not just financial assets (bits of paper). And "real option" theory was born.
One of the neatest concepts in real option theory is the option value of doing nothing.
Real option theory sounds really neat. But there's something missing, or left out, or just assumed to be there in the background but otherwise ignored. It's cash.
You can't just do nothing; you must always be doing something, even if it's lying on the sofa staring into space. If you don't invest in real assets, what are you holding instead? What do you compare the returns of real investment to? What's the alternative? What's the opportunity cost?
You can't just do nothing with your income; you have to spend it on something. If all things you could spend it on were irreversible, then you can't talk about the option value of doing nothing, or postponing a decision. You have to decide now. You could insulate your house with R20, or buy a new car, or buy a holiday, but none of those expenditures is fully reversible. You can't return the holiday after you have enjoyed it; you can't re-sell the new car and get anything like what you paid for it.
There is one thing you can spend your income on that is very reversible: cash. In fact, if we spend our income on cash, we don't even think of that as spending it at all. We think of that as not spending it. We think of holding cash as doing nothing. In fact, since we live in a monetary exchange economy, our income comes to us as cash anyway. So it's not like we make a decision to invest in cash today, and then reverse that decision next year. We have the cash already, and can decide to spend it now, or decide later to spend it later. Holding cash keeps our options open. Cash is the real real option -- to do anything.
Talking about the option value of doing nothing only makes sense in a cash economy. If we invest in insulation we cannot reverse that decision next year. If we hold cash, we can reverse that decision next year. Holding cash is to hold the option. Holding insulation is to exercise that option, so you no longer hold the option.
Cash is the most liquid of all assets. We measure the liquidity of all other assets against cash. One measure of liquidity is the cost of a round-trip, from cash, into an asset, then back into cash. What percentage of our cash do we lose by making that round trip? And that definition of liquidity is just another way of measuring whether an investment is reversible or not.
Suppose we live at a time when uncertainty is high, but we expect a lot of that uncertainty to be resolved soon. Just by waiting a short while we should learn a lot. That is when the real option value of doing nothing should be highest. That is when the demand for real investment should be lowest. But, compared to what? Compared to cash of course. Doing nothing means holding cash. That is when the option value of holding cash should be highest.
I think we have been living in such a time, and are slowly coming out of it.
Lots of people, Keynesian fundamentalists especially, will say "Of course! Didn't Maynard say that uncertainty creates liquidity preference?" And they are partly right, but mostly wrong. It's not uncertainty, but uncertainty that you expect to be resolved quickly, that creates liquidity preference. You can't learn anything about the dice by waiting, so you might as well place your bets and roll them now, and learn whether you win or lose. It's not the level of uncertainty that matters for liquidity preference, but the expected rate of change of uncertainty.
Maybe that's why investment is always the last thing to recover after a financial crisis. It doesn't recover as uncertainty gets resolved. It recovers when uncertainty stops getting resolved. That's when there's no point in waiting and seeing any more. Until then, people and firms will want to hold cash.
God forbid they ever announce that reliable crystal balls will be cheaply available -- next year. That would cause an instant collapse of investment, and a recession. Every student would wait till next year before deciding what subject to take. All the professors would be unemployed.

ただ単に何もしないことは不可能である。たとえソファに横たわって虚空を眺めている時でも、何かをすることは避けられない。もし実物資産に投資しないのであれば、何を保有しているのか? 実物資産への投資のリターンを何と比較しているのか? 代替の選択肢は何か? 機会費用は何か?
現金はすべての資産の中で最も流動性が高い。他のすべての資産の流動性は、現金を基準に測られる。流動性の一つの尺度は、現金から資産、そしてまた現金、という往復の費用だ。そうした往復の過程で現金の何パーセントが失われるか? この流動性の定義は、投資が可逆か否かを測定する尺度でもある。
我々が不確実性の高い時代に生きている一方で、その不確実性が間もなく解消すると予想しているものとしよう。少し待てば、多くのことを知ることができる。それが、何もしないことのリアルオプション価値が最も高い時である。それが、実物投資需要が最も低い時である。しかし、その場合の比較対象は何か? もちろん現金である。何もしないことは現金の保有に等しい。その時が、現金を保有することのオプション価値が最も高い時である。
多くの人々、とりわけケインズ原理主義者は、「もちろんさ! メイナードは不確実性が流動性選好をもたらすと言わなかったっけな?」と言うだろう。彼らは部分的には正しいが、大部分は間違っている。不確実性ではなく、すぐに解消されると予想される不確実性が流動性選好をもたらすのだ。待てど暮らせど、サイコロの出る目についての知識は増えない。従って、さっさと賭けてサイコロを振った方が良いだろう。そうすれば自分が勝ったか負けたかについての知識が得られる。流動性選好にとって重要なのは、不確実性の程度ではなく、不確実性の期待変化率なのだ。