When we lack humility.....

 Brothers and sisters, do not slander one another. Anyone who speaks against a brother or sister or judges them speaks against the law and judges it. When you judge the law, you are not keeping it, but sitting in judgment on it. 12 There is only one Lawgiver and Judge, the one who is able to save and destroy. But you—who are you to judge your neighbor?
13 Now listen, you who say, “Today or tomorrow we will go to this or that city, spend a year there, carry on business and make money.” 14 Why, you do not even know what will happen tomorrow. What is your life? You are a mist that appears for a little while and then vanishes. 15 Instead, you ought to say, “If it is the Lord’s will, we will live and do this or that.” 16 As it is, you boast in your arrogant schemes. All such boasting is evil. 17 If anyone, then, knows the good they ought to do and doesn’t do it, it is sin for them  James 4:11-17

We need to remember that this book was written as a letter.  So it flowed from one subject into another.  This passage followed verse 10 which exhorts believers to humble themselves.  Then the next thoughts from Brother James are demonstrating the behavior we exhibit when we DO NOT humble ourselves.........

The lack of humility -- that would be, duh, PRIDE -- shows itself in these three areas:

People, plans, priorities

Lack of humility results in our being

1.  Critical of people - vs 11,12
When we don't embrace our place in relation to God's rightful place, we tend to put ourselves on the bench as Judge.  We evaluate people's actions, ascribe motives to them, decide the appropriate punishment, and then, often we execute it ourselves.  Like a bailiff that usurps the role of the jury, the judge, and the jailer, all in one.  As though we don't trust THE Lawgiver, THE Judge, to address the problems in someone else's life, we assume responsibility of doing so.  Not that it's wrong to call sin "sin" - not at all.  The problem comes when we assume the role of determining motive and punishment.  That's pride.

2. Arrogance in plans - vs 13-16
Now I'm a planner.  I like to know my schedule and make plans accordingly.  I don't like to rush at the last minute to do things that could've been taken care of in advance.  Is this passage condemning such contemplations?

Plenty of other verses commend and exhort planfulness.  Proverbs 6:6-8 and Proverbs 10:5 to name a few.

Rather, it's calling us to examine not only the making of our plans but especially the "why".  Notice the motive in verse 13 -- "to make money".  Other translations say "to make a profit".  The lack of humility is demonstrated when our goal is to advance our own agenda rather than submitting to God's plans for our time.

3.  Setting of priorities - vs 17
When my life is characterized by pride (self-focus) instead of humility (God-centered), I am prone to ignore the promptings or conviction of the Holy Spirit.  And then I don't do what I know to be right and/ or I do what I know to be wrong.  That is sin.  Of omission or commission.  It's sin.  And it's rooted in pride.

SO, how can we walk in humility instead of pride?  If these verses reveal pride in us regarding our attitude towards people, our pursuit of personal agenda, our insistence on our own way - what we we do instead?

Go back to verse 10.  Get in the presence of the Lord.  Soak up who HE is and inevitably we see who we are NOT.  Confess the sin His Spirit reveals.  Ask for His transforming power. 

And ask Him to point out every manifestation of pride every time it occurs.

Then repent.  Change directions.
 Give grace to people instead of condemnation.
Ask the Lord for His directions instead of your own.
Respond in obedience to what He shows you is right.

Pride is destructive. 

Humility is exalting.  Right into His presence.
And there, and only there, do we find fullness of joy.