1.  Some people like working on a certain job.

2.  Some people are fond of working at a certain job .

3.  It is secure and comfortable for them to invote themselves in a certain job.

4.  Some people like to do a certain job, they take it for their career .

5.  When they go in for a certain job, they alway want to change it, perhaps because they long for some other job with much money.