In terms of human behavior (animal behavior) and survival skills, we have a combination of kinds of memory that allow us to remember how to do certain activities, some being as simple as walking and talking, some being more complex, like riding a bike, ice skating, doing a math problem, or cooking a meal. When you learn how to do something, you learn a set of conditioned responses or apply unconditioned responses that make up the entire action. Conditioned responses are those which you have been taught (through various methods), and unconditioned responses are those which are preexisting, possibly instinctual. The process of acquisition, the learning itself, is then reinforced by your successful completion of the activity. How well you learn something depends on how often you do it; practicing an activity will put it into your short term memory, where it will eventually be transferred into your long term memory. Practicing also reinforces an activity in your muscle memory, for example, how you don’t really have to think about what you’re doing when you’re walking; your muscles just know what to do because they do it so frequently. When you remember how to do an activity, it could be because that memory is stored in either your long term or your muscle memory. The process of retrieval for that is easy. If retrieval is not easy there are two theories as to what you may have forgotten that thing. The first, the interference theory, says that new memories are prevented from being encoded because of the presence of old memories. This can be either pro- or retroactive, the former meaning that old information doesn’t allow new information to be remembered, the latter meaning that the most recently learned information prevents you from recalling things learned earlier. The other theory is the decay theory, which says that memories disappear or “disintegrate,” like a sort of neural atrophy. The idea is that the neural connections that allow you to remember things have weakened because of disuse (for example, you might not have had a reason to remember how to skateboard between the time when you learned and now, but you may have had some reason to remember how to ride a bike, so that memory is stronger and more accessible). The last memory phenomenon is the idea of a memory being on the “tip of the tongue,” when you cannot exactly locate the memory. Your skating example is similar to that; sometimes you just can’t locate a memory for some reason, but sometimes it falls into place easily. The best method of being able to remember things is considering the way in which you learn the information. Conditioning and behavior modification are some of the strongest learning techniques, along with Rote learning (in which you learn in a list or ordered process, and, as a result, you have difficulty completing the task or list in an order that you didn’t learn it in – think about learning a song), rehearsal/practice, and social or observational learning. Let me know if you’d like to learn more about those!