Why Do Investors Ignore Cash Sitting Idle In Their "Return" Calculations?

[Bryan Hancock]

I have observed that investors consistently IGNORE the fact that their time sits idly in a bank account when they tout their "AROI" on their projects. This is quite puzzling to me and I was wondering why people do it.

People often let cash sit around waiting for the home run deal that only comes along every few years instead of having it in play in good projects consistently.

Why is this? Is it mainly to impress people at cocktail parties? Ideas? How much do you estimate this saps REAL returns for most portfolios?