In the psychology of memory this is one of the two ways that long-term memories can be interfered with.
Proactive interference is when old information interferes with new information. (Proactive = acting forward into the future). Trying to remember one phone number isn't (too) hard, but the second one will be harder, and the third even worse. Old info builds up static that messes up your newer memories.
The more info the harder it is to remember it all. Why bother to point this out? Because there's another kind of interference to contrast it with -- retroactive interference.