When I think about it, the greatest barrier to human productivity is the incorrect use of the 24-hour day.
How we spend our time during the 24-hour period can be the difference between high and low productivity. Much time can be wasted and disproportionately allocated.
We have the freedom and discretion to choose how we allocate the available blocks of time to the things we want to do . . . up to a point!
Think about it. We need to sleep, to prepare meals and eat, to travel, to work, to study, to exercise, to go to the toilet or bathroom to wash and bathe, to interact with friends and family and other people. We need time for personal care and quiet reflection, for relationships and intimacy, time to shop and manage our financial affairs, etc etc. Some of these are discretionary and some are compulsory.
There are occasions when time must also be re-allocated from one activity to another, such as during preparation for examinations, attending a funeral, physical illness and meeting assignment deadlines. We can choose how we shorten or lengthen these blocks of time for activities such as sleep, which is probably the easiest to sacrifice around examination time when working late into the night seems such a good idea.
It is a good exercise to draw a 24-hour day timeline and consider how you spent it yesterday. Compare this with your 24-hour timeline from several months ago. Are you allocating enough time to sleep and exercise? Are you combining blocks of time such as meals and study? Have you decided not to allocate a block of time for exercise?
You will be more productive if you do.