When dealing with children, there is a constant push and pull for power in all areas of their lives. This is not a bad thing. (Would you rather see your child coalesce to every request you give? What kind of independent thinker are we raising here?) The importance in negotiation with children, as well as them negotiating with us is to leave tears out of it and once they dry, to return to logic and reason.
Today, my daughter was having problems with her math assignment, and I explained to her how to do the problem. But she wasn't grasping the concept, after I explained it 3 times in two different ways. She didn't ask any probing questions, just grunted a bit and started to cry when her grunts for help weren't effective. I refused to provide her the answer and she continued to struggle. I occasionally gave her tips, but refused to do her homework for her, I had already passed that grade.
She eventually got it, and the experience connected more synapses of her brain, while also making her streak of usual independence continue, despite the early tear negotiation. It is a success for both of us, me not giving in, and her not becoming used to having her emotions be used to get things she didn't earn.
Parents also have this issue of using emotions to get responses out of their children, which isn't helping the cause either. Children are the great imitators of their parents or if no parents are available, the closest grown up where an attachment or connection can be developed. Moms that cry in front of their children because they are being bad or dads that use their anger to get obedience are creating the same "Because I told you so" or "you don't love me because" kind of empty lessons that will come back to bite kids later on in life.
Do you want your child being an emotional leaf blowing in the wind? The world would be a much more beautiful place if we all learned to use logic and reason rather than holding our children captive to emotional whims.