A biblical conception of human depravity doesn’t imply that human nature is as evil as it can possibly be. Although we are often bad, we could be much worse. People often do good and generous things.
Rather than teaching that every aspect of our nature and personality is as bad as they can possibly be, the doctrine of depravity teaches that every part of our nature is tainted with original sin. Therefore, although we are always potentially more evil than we are in actuality, everything we touch is tinged with sin.
The Evangelical Dictionary Of Theology (Walter A. Elwell, Editor) gives this brief definition of depravity.
Positively, total depravity means that the corruption has extended to all aspects of man’s nature, to his entire being; and total depravity means that because of that corruption there is nothing man can do to merit saving favor with God.