The reason is human nature. Since people have no reliable sense of time they do not know how they actually spend it. But they believe that they do! Drucker writes about one of his client. This president of a company was sure that he spent 1/3 of his time for his superiors, 1/3 for important clients and 1/3 for work with the subordinates. However the time log had shown that he spent only an insignificant part of his time for these 3 important blocks. The reason was that he understood that he should do it but his feeling of time deceived him as it deceives all or almost all people.
So, what can we do? Drucker recommends that you periodically record your actual time spending. It's OK if you have a secretary that can record your time for you, but most of people find it's too boring to record their time. And it is not because we lack the discipline but rather as modern research shows "we have a limited amount of attention". The more attention we pay to time recording the less attention we can pay to work. As time manager expert Hillary Rettig admits writing about the time recording in her article for Microsoft "ChannelBiz" "it's probably a great idea, but I've never had the patience for it."
I also have never had the patience for time recording. According to the research (Barkley et. al., 2001) most of us have no such patience. Fortunately I can write programs. So I made the program Activities and Priorities, which makes recording how one spends time much easier. Why? First, no need to interrupt your work for the time recording because the program is tolerant of your errors in the time values. Second, in dynamic time management you may operate with only a few most important activities (This will be explained in this guide later). If you consolidate time for these important activities, as Drucker recommends, into large continuous blocks it becomes much more easy to remember how much time you spend for each of the activities.
"There is never much resemblance between the way these people thought they used their time and their actual records."(Peter Drucker)
"Effective executives start with their time, finding out where it actually goes." (Peter Drucker).
"Given the limited storage capacity of attention and working memory systems, the more an individual must allocate attention to nontemporal information, the less they can allocate to temporal processing..." (Barkley et. al.)
"Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. THAT'S relativity." (Albert Einstein)
«"If you knew Time as well as I do" said the Hatter, "you would't talk about wasting it. It's him... Now, if you only kept on good terms with him, he'd do almost anything you like with the clock."...
"Is that the way you manage?" Alice asked. » (Lewis Carroll)