The present is more attractive than the future, especially when there are rewards in the present. Therefore humans procrastinate - or put off doing an action - when that action will cause them discomfort. The discomfort can be that they will have to be mentally uncomfortable, like having to make a tough decision or delay gratification, or it could be physical.
Examples:
An employee knows they need to get started on that quarterly report. But the thought of having to struggle to pick the right words and search through other documents to find recent numbers, makes them delay getting started.
An individual hates needles and does not want to go to the doctor because they know their doctor is going to draw blood. Therefore they keep putting off making the appointment.
A farmer wants to put fertilizer on their crop but it’s unpleasant to do. So everyday the farmer plans to do it tomorrow.
What it is not:
Putting off thinking about something uncomfortable - that is ostriching.
