I was talking to one of my colleagues that I can trust on. He was giving me tons of advise in the work. I admired his experiences being in the different project in different countries. Our conversation was about how I felt that I had a subordinate that some of his works are done by me and I was complaining a little about it.
My friend told me that it was my fault. I created a work environment that making my subordinate comfortable with his current tasks. Any additional tasks that are given to him would result into complaints. And all of these were my fault. My friend added that it is a human nature that are reluctant to a change. He gave an example that during weekend without plan, he will fell tired and just want to stay at home. If all of the sudden, your son or spouse ask you to do something, you will be reluctant to do it. This applies as in work environment.
In summary, my fried told me to impose additional tasks to my subordinates with proper planning. Adding the task step by step with proper planning will result into less resistance. And the additional tasks will become his daily routine that he will be comfortable with. My friend added "If your sub-ordinate complains, just disregard it and push him to the limit. Tell who the boss is!".