It is commonly known that in physics the harder or faster one pushes against an object the more resistance is produced in the opposite direction. We commonly accept this without even thinking about it. However, there also exists another form of resistance in the field of psychology or behaviorism. That rule is simply; The harder one tries to push someone else to perform a certain behavior the harder the other person will push back with the exact opposite behavior. In other words, the more you want someone to do a certain thing the more that person feels compelled to do the exact opposite. This phenomenon is usually exacerbated when there are emotions and relationships involved.
Examples of this are usually seen among interactions parents have with their children. However, these interactions are far from being limited to paren/child interactions. For example, have you ever tried to coach your son or daughter? This is a typical situation that most parents find themselves in. Wanting to pass down that knowledge they have gained to their kids. Usually, the son or daughter fights this tooth and nail. As a parent, you don't realize that this is not a personal issue against you but rather your child's natural reaction towards feeling controlled. Some of the best coaches out there have resorted to hiring fellow coaches in order to coach their own kids for this reason alone.
Spouses also will experience this "resistance" phenomenon in similar ways. One spouse pushes the other to become more fit or eat healthier and what inevitably occurs is the exact opposite behavior. Again, the resistance is not as much as being intentionally defiant as it is being a normal human reaction to someone exerting pressure on another. It really doesn't matter if that pressure is intended for the benefit of the other person. It will be perceived as unwanted and the resistance phenomenon will take hold.
Resistance training in the psychological sense is akin to resistance training in the physical sense. The more you push the other person the more resistance is created. The individual you are trying to help actually builds up a negative reaction to your efforts. This is not just true in parenting circles but also in all those relationships you find yourself in.
It is much better to lead or pull than to push. Pushing someone in your direction will only lead to more resistance on their part. However, using that person's already present momentum to move them forward in a more correct direction is much more efficient strategy and produces greater results in less time.