Sentence:  A basic human characteristic is the preference for consumption today over consumption tomorrow. Jam today is always better than <WSD>jam tomorrow</WSD>, unless sufficient incentive is offered to forgo the immediate enjoyment of today's jam. This is not because of uncertainty about the likely receipt of <WSD>tomorrow's jam</WSD>, but merely a property of the passage of time. 
Meaning of the word marked with <WSD> tags:  Availability of a resource at a future date.