One of the most satisfying jobs in my career was as a student when I stacked shelves in the dairy section of the local supermarket. No, seriously. I worked there for 7 years and I often felt a sense of achievement after a day of work having unpacked pallets of stock and seeing the fruits of my labour as I looked around at the full shelves. The work was highly tangible, fairly simple and repetitive, but enjoyable. But the work of a knowledge worker is quite different to that - it is often intangible, complex, ambiguous and varied, and carries pluses and minuses by way of comparison.
Do you ever hear yourself say or think that you feel like you have achieved little in a work day and would like to just get some real work done? Perhaps what we are lamenting when we say that is the lack of a tangible output that day and therefore we feel like we are not contributing to the team in a meaningful way or earning our keep.