Let's say you are with a friend and that friend asks what you did last Saturday. You only have a few seconds to find the information in your memory. If you take longer than that, then it halts the conversation. If you are a person who believes they have a weak memory, then while this is going on your mind is generating negative self-talk: "My memory is so terrible" "I just don't want to embarrass myself" etc... It becomes a self-fulfilling prophecy.

Now, let's say you are on your own and try to remember all that you can about last Saturday. This is much more relaxed. And it is much more in-depth. You could spend an hour thinking about it if you really wanted to. You could even think about it for a while in the morning, let your subconscious work away at it during the day, and come back to it in the evening. Doing memory exercises like this gets those neurons firing and can strengthen memory so that it becomes easier when you do use it as part of everyday life.