In my opinion that it depends on so many reasons such (No changes, low salary, no one appreciating his work, doing complete work by himself, no challenges, same daily routine and no training course and improvment ...etc.).
At the end, all those reasons are falling under two points:
1- Leaving because of Personal Needs (which you may find somewhere else)
2- Leaving because of Work Environment (Not about personal needs but it can be an extra thing or advantage where it is not available at his recent work, and they employee would leave and look for it at another place) such as a higher position, good brand company ... etc.)
Regards,
In my opinion these are the points that will lead you to quit your job:
1- When you find that the management is not appreciating your work
2- lack of facilities (i.e bonus, food, transportation etc)
3- when you find that you have to do your regular work daily with no changes