Before the coming of Christ this sort of contrition was held up to men as the only penance, the only means of salvation; and it must have been an easy one to fulfil. How much more, then, may a Christian who leads a God-fearing life and strives after perfection feel assured that he possesses such contrition when he prays God for it, reflects earnestly upon it, and then recites the act given in his prayer-book. Suppose, for instance, that perfect contrition were really wanting, then imperfect suffices for the remission of sin in the confessional.
Imperfect contrition is such as is born of the consideration of the heinousness of sin, its evil consequences,or the fear of hell and purgatory.
A few moments' reflection must easily produce such sorrow in a Christian soul. From what has been said it follows that the sorrow required for a valid and efficacious confession is by no means so hard to obtain as many suppose.
Link (here) to the mentioned portion of the book entitled, The Way of Interior Peace: Dedicated to Our Lady of Peace. by the Jesuit Fr. Edouard De Lehen, S.J.