For successful completion of a work, a criterion may be required for individual to scale and assess her/his pursuance with regards to the desired outcome. This very criterion could be of a virtual or real nature.
Thanks to all: I differentiate the issue of half-full and half-empty in this way: I suppose half-emptiness instigates potentiality resulting forward move. On the other hand, half-fullness because of its positiveness may halt even little while. Anyway, any case may be defendable, depending on the taste of an individual.