Denial means the act of denying. To deny means to refuse to oblige someone with something that he wants. Denial generally spoils your equation with the person, whom you refuse to oblige. The cause of denial may be just and satisfactory, or may be completely invidious. Denial of justice in court cases is a shame on the judiciary system of a nation. Justice is not granted in many cases and this justice delayed, is justice denied. If you are delayed by someone, you get an idea that you'll be denied a wanted favour by that person. In the words of C. North cote Parkinson, “Delay is the deadliest form of denial.”
A satirical remark was made by Mark Twain, keeping in mind, the act of denial. Quote verbatim, “Denial ain't just a river in Egypt.” No one likes to be denied a much wanted favour. The bible says, “Do unto others, as you want others to do unto you.” So, don't deny someone anything that is justified and very much desired by them, if you want others to oblige you with a favour, too.