I think it has to do with more work being "creative", in the Richard Florida sense, of being problem-solving oriented. It is much easier to estimate the time needing to complete tasks such as "milk the cows" or "build a shed", because 1) You do them repeatedly and can learn, and 2) The bottleneck is not thinking, but the manual labor, or the time it takes to use a given machine.

I might be irrational, but I always estimate problem solving time to be much smaller than what will actually be needed. Even afterwards, I will usually consider much of the problem solving time as time wasted, because I should have been able to do the task much faster.

taking too much on due to technology allowing us to do more, getting stressed with it, not being able to stick to time management system.