Poor in spirit suggests that they have a proper understanding of where they are spiritually, and are therefore broken and repentant over their poor condition of sin and depravity. It is those who are acutely aware of their sin who will come to Christ for their salvation...those who are blind to their sin are of a high spirit though they deceive themselves.
..."Those who are well have no need of a physician, but those who are sick. I came not to call the righteous, but sinners." (Mar 2:17)