I feel so sad today

Sad for myself. Nothing to do, nothing I want to do. Re-read "Thoughtful Interaction Design". In the first chapter, Erik Stolterman said:"Working with design means that you continuously need to define and redefine what you think of as good design. It is a never-ending process of thoughtful reflection."

As human, we need to define and redefine ourselves, and this process is never ending. That is why Marty said that the learning process is painful.