The telescoping effect is the tendency to have inaccurate memories concerning how recent and frequently events occurred. There are two main categories of telescoping effects: backward telescoping is the belief that recent events occurred further in the past, and forward telescoping is the belief that events that remote occurred more recently. One theory (that only explains forward telescoping) is Time Compression theory; the idea behind the theory is that time subjectively feels shorter than it is in reality. Another theory which may explain the telescoping effect is variance theory, which argues that we have uncertainty about memories, and this uncertainty increases with more distant memories. Neither of these theories fully explain telescoping, however.
An important implication of telescoping is an overestimation of frequency. This is because events that are too far in the past to occur in a timeframe are mistakenly included, and events too recent are included as well.
For example, you are asked to estimate how frequently it snows in December in your area. Due to forward telescoping, you are likely to include November snow. Similarly, due to backward telescoping, you are likely to include January snow. As a result, you will overestimate the frequency of snow in December.