Author Richard Powell believes that the Japanese concept of wabi-sabi comes down to these three simple realities: "Nothing lasts.  Nothing is finished.  Nothing is perfect."  They are based on the the three marks of existence in Buddhism which are suffering, impermanence and the non-self.

To me this understanding of wabi-sabi is adequate as an abstract concept but the thing about wabi-sabi is that it is the manifestation of the abstract which makes it wabi-sabi.

There is a famous story about Sen Rikyu who was the founder of the tea ceremony.  Rikyu's son hosted a tea gathering for his father at his home.  He had his wait staff clean the entire estate to perfection and he himself looked after the details for the ceremony.  Everything was perfect.  When Sen Rikyu arrived he noticed how pristine the roji or walkway was to the chashitsu or tea house.  Rikyu paused and said, "Something is missing."  At that moment his son realized his mistake and shook the tree so that some leaves fell and landed on the roji.  Rikyu then smiled and said,"Perfect."  His son understood the abstractness of making things perfect, but it was the imperfectness of the leaves which made it wabi-sabi and thus imperfectly perfect.

I would complete Powell's assertion this way:

Nothing lasts. Nothing is finished. Nothing is perfect. Now go do something.

The first three statements are abstract which could bring about a sense of disillusionment, but it is the last statement I think brings it all together.  Yes, nothing is permanent, finished or perfect but that is precisely why it is still necessary to do something.