What is desirable and undesirable change?

What is desirable and undesirable change?

Desirable change :
The changes which are desired(need) to be change are called as desirable changes.
Ex: Change of milk to curd, reopening of fruits…etc

Undesirable change :
The changes which are not desired to change is called undesirable changes.
Ex: Earthquakes, hurrcanes, tsuanmi …etc