Imagine coming home and opening your fridge to find a jar filled with your favorite juice. After taking a sip, you realize that the kind soul who prepared the juice added too much water, and there's not much you can do to fix it — removing water from juice is a complicated process. However, if instead the juice-maker was too stingy with water, you can simply dilute the juice with extra water and enjoy a perfect refreshing drink.
A similar phenomenon happens with the risk of financial assets. If an asset has too little risk, it is complicated to “remove water” and make it riskier, usually through leverage. On the contrary, if the asset is too risky, it is straightforward to dilute it with cash equivalents, such as short-term Treasury Bills, or T-Bills.