Why is it reasonable to assume $1.00 in excess cash/cash flow today can/should/will be more valuable in the future? Because the U.S.federal government provides insurance to commercial banks to guarantee that all persons with a bank account will receive some kind of investment return on their cash balances. We are assuming this only for theoretical/analytical purposes for illustrating basic investment principles. Because there are thousands of investable assets available; most adults produce some amount of cash in excess of their total expenses; and, most adults invest in some kind of investable assets that earn a positive return. It is not reasonable to assume $1.00 in excess cash/cash flow can/will be more valuable in the future because inflation causes the value of currency to depreciate