"Disposition" is the mood people are inclined to have. It's how we're predisposed to be. Some are the full cup and the others the empty; the full cup being positive and the empty the negative. The negative disposition is the tendency for a person's interaction with others and the self to be of a critical nature. "Nature" implies we are the way we are because we're human. God has no nature, but a super-nature. Hence, having a nature is inborn, and is part of our genetic makeup.
God's super-nature is "good". "Only God is good!" (Luke 18:19). We all fall short of goodness and being critical is one failing. Therefore, mankind can only endeavor to be good. That feeble attempt is the act of attempting to live a righteous life, that life to be an emulation of how Christ lived his. In that passage, since Jesus IS God, then only Jesus IS good. Albeit, we all will miss the mark, we all should attempt to be good, but not of ourselves, but in obedience to God in an attempt to do God's will.
Jesus was not an overly critical fellow. Being like us in form, he was tempted to be overly criticizing, but because he is God, he was genuine: he had both real and abounding love and concern and was fair at the same time. With those who were rebellious, Jesus criticized out of love, but never to condemn. However, those with negative dispositions condemn with their critical nature even those that they may love!
It is called: getting up on the wrong side of the bed. However, some people seem to get up everyday on the wrong side! Sure, we all our sometimes critical of others and treat others cruelly, but others do that as a lifestyle. A common example is for one who says "It's a great day!" Those disposed to negativity would reply, "What's so good about it?" The correct answer is that both are alive, well, have food and should appreciate that. Those with negative dispositions fail to appreciate what they have, and even when they get more, are still unappreciative.
I appreciate everything I have because much of my early life was having not. I don't deserve what I have, but am thankful. Thankfulness is a remedy for negativity. If one isn't happy with their friends, then they can't be happy. Before happiness can be, people have to be happy inside. Those with negative dispositions seem to never be content with what they have. In essence, they expect more whether they deserve it or not, but more never satisfies. There is a spiritual problem which exists that nature can't resolve!
Psalm 118:24 ( ESV) "This is the day that the Lord has made; let us rejoice and be glad in it."In short this says: be content for where you are today is due to God.
Some look toward others to provide contentment. Others can never make one content. Contentment comes from God and that requires communion with God. Some are predisposed to a critical nature because they are out of fellowship with God. He is the source of goodness, and without God, men are inclined to be evil. Being negative is not a righteous condition. Indeed, negative people are out of God's will, but he can bring them back if they are willing to change. If a person is unhappy right now with what they have or who they are or with, that can be changed! It's not to complain about what's lacking, but being joyful in what one has!
I'm not a proponent of positive affirmations or the prosperity gospel. Sometimes things won't go right when we are persecuted, but why persecute others with a negative disposition toward life? If you want to be happy and content, make others happy and content. Misery begets misery. Never have another person "walk on egg shells" just to not set off your fuse! Yes, some are set off at the most benign things, even positive comments because they are predisposed to be critical.
Usually, those with negative dispositions aren't loving. They are who they are because their nature is to be unloving. The only cure for not being loving is to change face; become more loving. That's empathizing with those to whom you're overly critical. It's building others up:
Ephesians 4:29 ( ESV) "Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear."God calls us to have a positive disposition by building others up. It's impossible to build others up by being overly critical. In fact tearing down makes both parties the victim: no one enjoys being slaughtered by the tongue and those who use the tongue to destroy are in effect self-destructive. So that the other will not be happy, those negative will sacrifice their own happiness!
Of course there are solutions to all problems. Solve the problem or live with it. Living with problems is not living. Therefore, solving the problem requires change. Change has two directions... make the change your way or God's way. Your way has a negative penalty. God's way has a positive reward. Overcoming negative personality traits is hard work, but it's expected by God and rewarding to those who change!
If you're miserable in life being you, then become someone else. Be how God wants you to be and the result is joy. Who would want to live a life without joy? Some choose that!