If you observe the people around you briefly, even for a few hours, you will see a very important characteristic that prevails most of them: "The disease of being the one saying the last word"…
In order to see this disease in people, it is not necessary to be talking about very important points; sometimes a memory that is shared, sometimes a recipe of a tasty food, sometimes a television show watched, sometimes an ordinary casual incident, sometimes a newspaper article one reads might cause the occurrence of this illness. Of course someone, who acts this way even during such casual daily conversation, would not leave the last word to anyone else when much more important and vital matters are discussed.
Most people might be defining this habit they have as "having a distinctive personality", "participating", "using his wisdom" or as "making his personality felt". However, no matter how he names it, the habit of being the one saying the last word is a very important flaw.
Moreover one can really be very smart. He might be more experienced than everyone else, he might be more far-sighted and he might be someone who can think more details. However even if all those apply, a person's trusting only in his own mind, being persistent in his own account and disregarding anyone else's opinions, is a mistake from lots of angles.
First of all it is "egocentricity", that is "the feeling of supremacy", that lies beneath a person's being uncomfortable unless he says the last word. The "desire of being above everyone else" in their lower selves, causes such people to strive to be the only voice over the people around them. They want only the things they say to be applied, they want every incident to be handled with their methods, everyone to act by their rights and wrongs, they want to be the person everyone respects and honors the most. When they see someone acting in the contrary, such people consumed in egocentricity feels very uncomfortable with that. And when they encounter someone else who also has the disease of being the one to say the last word, they get into a serious conflict and competition with that person.
They face up adopting many attitudes that are not compliant with good morals in order to get an edge, to be justified, to get their opinions through and to be the one to say the last word. They continue this bad habit of theirs no matter what; sometimes by copping an attitude, sometimes by using sharp wordings, sometimes by interrupting others, sometimes by saying offensive and barbed comments, sometimes by turning a nice conversation into a discussion.
Whereas the good morals necessitate them to handle the matters, even if they know what is best under that circumstances, firstly by approaching their Muslim brothers with love, respect, 
modesty and tolerance; by propitiating them and by honoring them hypocoristically. There are many nice ways of doing the right thing. And a person's disregarding all these moral necessities and bursting out what he thinks to be right, is not compatible with the moral values of the Qur'an.
Moreover it is very difficult for someone to be the one who always knows the absolute right in everything. There are many matters that one can learn, benefit from, ask for advice and take as an example from the people around him. Sometimes a detail he can never think of might occur to someone least expected. Allah might show everyone a different aspect of a point and inspire each of them to think with different methods.
Consequently not accepting anyone else to have a say in a matter, not listening to anyone else's ideas and always wanting to be the one that finalizes the matters, is on no account a reasonable moral attitude.
Allah reveals in the Qur'an that "He gives the knowledge to anyone He wills to give" and that " there is a knower over everyone with knowledge":
... We raise in degrees whom We will, but over every possessor of knowledge is one [more] knowing. (Surah Yusuf: 76)
As the necessity of the moral values of the Qur'an, even if a Muslim is the wisest person on earth, he should behave humbly towards his Muslim brothers. A Muslim, even in matters he know best about, must leave the last word to others as a necessity of this morality and respect others' opinions and behave kindly, courteously and pleasantly.
No matter how much one can be sure of himself, he should know that there will be no abstinence when he does not say the last word. If a person is adopting a good moral behavior by acting by the approval of Allah, he should be sure that Allah will always lead him to the best choice and enable him to do the best, and he should never begin to suspect this.
Allah had revealed this truth to the Muslims in the Qur'an :
"Those unbelievers say, ‘Why has a Sign not been sent down to him from his Lord?’ Say: ‘Allah misguides whoever He wills and guides to Himself all who turn to Him" (Surat Ar-Ra'd: 27)
