Stop trusting in mere humans,
who have but a breath in their nostrils.
Why hold them in esteem?
(Isaiah 2:22, NIV)
All humans breathe with nostrils. So, should we distrust all people?
The question is not whether or not to trust people, but whether or not to put your trust in people. Obviously, people are quite capable of telling the truth. However, trusting in people to meet your needs is where the problem comes in. People are mortal and finite with limited power. Indeed, they have "only a breath in their nostrils". This may be suggesting that everyone is living breath to breath. If you put your trust in your parents to provide for you or get you out of trouble, you should be aware that there is no guarantee that they will be alive tomorrow or will have the power to help you.
God, however, is infinite and self-existent. He will be around tomorrow and has all power to meet your needs whenever and however He chooses. Thus, it is prudent and wise to look to God and trust Him for your needs and life--not a fellow human being whose life is but a vapor that appears for a little while and then is gone.
Chapters 2,3, &4 all go together in Isaiah.
Isaiah is lamenting the fact that God has apparently abandoned the Nation of Israel and is attempting to get his Nation to once again trust in the Lord.
In chapter 2 especially he is telling them that they should not put their faith in any earthly government since they all come into prominence and ultimately fade into oblivion. But God is always preeminent and dictates who will be in power at any given period.
That is the point of verse 22 why would they put their faith in a temporary government instead of almighty God.
That same question could be asked of any period of time.
Isaiah is pointing out that even the Earth is temporary, but Heaven is eternal.
I agree with the other answers, but I thought I would add some historical context for Isa 2:22...
I like the KJV of this better, it makes more sense to me.
Cease: Cease depending on mortal man; he is of little power compared to God. Trust not in the arm of flesh.
This scripture explains Isaiah 2:22 quite well