Brethren, I count not myself to have apprehended: but this one thing I do, forgetting those things which are behind, and reaching forth unto those things which are before. - Phil 3:13
The hinderance to the new is the old. Until we learn to let go of the old things, we may never attain the level of the new. It is essential that every man sustains the ability to let go of things of old and reach out for the new.
The fact that it is behind you means, it should not have a place in your present.
Do not permit your past to dictate your future by tampering with your present.
Are there mistakes you've made in the past? Learn from it and move on to perfection.
Are there achievements you've accomplished in the past? Do not dwell in it, there is more.
No matter what happened in the past, let it remain in the past and focus on the future ahead.