Why is a pure-discount government security (one that does not make coupon pays interest at maturity, and

Question:

Why is a pure-discount government security (one that does not make pays interest at and sells at a discount from par) with no risk of default still risky to an investor whose holding period does not coincide with the date of the security?
Coupon
A coupon or coupon payment is the annual interest rate paid on a bond, expressed as a percentage of the face value and paid from issue date until maturity. Coupons are usually referred to in terms of the coupon rate (the sum of coupons paid in a... Maturity
Maturity is the date on which the life of a transaction or financial instrument ends, after which it must either be renewed, or it will cease to exist. The term is commonly used for deposits, foreign exchange spot, and forward transactions, interest...