Proactive interference is the disruptive effect of prior learning on the recall of new information. Old memories get in the way of new ones.

A person who has driven a car with a manual transmission may, when first driving an automatic, reach for a clutch that is no longer there. Students who learn a list of words and then learn a second list often find that items from the first list intrude when they try to recall the second. The more similar the old and new material, the stronger the interference tends to be.

Proactive interference is one reason that learning successive similar tasks can be frustrating. It is the counterpart of retroactive interference, in which new learning disrupts the recall of older material. Spacing learning, using distinctive cues, and allowing time for consolidation can reduce the impact. The phenomenon demonstrates that memory is not a set of isolated traces but a system in which traces interact.

What you already know can make it harder to remember what you have just learned.