The forgetting and time most likely refers to the forgetting curve done by Hermann ebbinghuas, his forgetting curve describes the decrease in ability of the brain to retain memory over time. The issue was hypothesized by Hermann Ebbinghaus in 1885. Which is an equation meant to show the rate at which things are forgotten.
Which is: R = e-t/s
Where R refers to memory retention, S refers to relative strength of memory and t refers to time.
But, that said, not all memories follow the forgetting curve as there could be various other factors in play, such as noise and other environmental factors. Because of their influence on what information is remembered, not all memories are affected by detrimental effects of interference.
Hope this helps!