No, it is sometimes an evidence of lack of faith. But generally it arises from a very proper sense of the heinous nature of our sin. Though God forgives, and we rejoice in the fact and adore him for his marvelous magnanimity, we cannot forgive ourselves. There is a very touching expression in Mark 14 -.72 which intimates that Peter's memory of his denial of Christ was life-long: "When he thought thereon, he wept." The other Evangelists speak of his weeping at the time, but Mark, who probably knew him well in his later years, phrases it differently. Yet, though Peter may have continued to weep at the thought, he could never have had any doubt as to his being forgiven.