People do not want to accept it when they have made a bad , not to be confused with "bad" painting, painting nor do teachers tell students when they have made a bad painting. Making a bad/ unsuccessful painting is ok, its part of the growth you have as an artist. You have to know what does not work so you can learn what does. There is such a thing as a unsuccessful painting or work of art in genera. There are a number of ways a work does not work, and it has nothing to do with a TV show with host of self proclaimed experts. It is different for every piece based off intention, the success of the medium, size, color, composition, texture, style, paint quality/ material quality. Within these categories there can be a number of things incorrect, or wrong which is detrimental to the piece. A piece being unsuccessful is not an opinion about the piece but is pointing out to the artist where they can improve themselves or think about alternate ways of creating. Critiquing a work is not critiquing the person.