Sour grapes = the fox says that then grapes up in them vines are sour, so to not feel pain for not having them.
Disdain to worldly pleasures, to small comforts of life, to anything positive that you do not have.
This disdain can be aesthetic, which is above (or be,ow) criticism. Yet this doe snot make it rational. It can be a matter of priorities - I have more important goals to pursue. This is ok. But limited. Having more important things to do is not reducing the value of any other project. It merely makes you invest elsewhere.
The last reason for devaluing is psychological. If i miss something, it feels better when i think it is worthless. This is very legitimate. Self delusion can work wonders at times. But like all self delusion it's has a price. The biggest price is the developed inability to enjoy the things you contempt. This is a curse of poverty following being poor. One is not only poor now, but he also convinces himself of the blessing in his state that he loses the ability to enjoy anything rich, or the willingness to improve his lot.
There are so many ways to enjoy and to experience life. It is stupid to neglect the ways that are not part of our own repertoire.
PS. We are naturally concentrated on some pleasures and goals, but positive concentration is it not active neglect and contempt to anything out of our focus.