Often it is easy when we look at biblical characters to find them unimpressive. We have the tendency to judge their failures rather harshly.
The reason is we often fail to understand the magnitude of our own issues. We frequently fail to find courage to do the right thing when the cost is relatively low and yet somehow judge those who slipped in moments of possible life or death.
It is our sinful nature to judge ourselves better than we are. The fall makes self judgement difficult.
We give ourselves the benefit of the doubt, but not others. When we come to the bible we must always remember when we see the failures of others that these are the tendencies within us.
And many of the biblical characters whose failures are described are people of greater faith and greater courage than we have. It is easy to fail to learn because we think of our self better than we ought.
God's grace is always sufficient.