The memory bears evident marks of sin and corruption. What is good and worthy to be remembered, makes but slender impression, so that impression easily wears off; the memory, as a leaking vessel, lets it slip. As a sieve that is full when in the water, lets all go when it is taken out--just so is the memory with respect to spiritual things. But how does the memory retain what ought to be forgotten! Sinful things so bear in themselves upon it, that though men would sincerely have them out of mind--yet they stick there like glue! However forgetful men are in other things, it is hard to forget an injury. So the memory often furnishes new fuel to old lusts; makes men in old age remember the sins of their youth, while it presents them again to the mind with delight, which thereupon returns to its former lusts. Thus the memory is like a riddle--which lets through the pure grain, and keeps the refuse.
I always think, "why can't I forget those horrible sins!?" Makes sense to me!