I learn something when I am doing my work last week that we need to write what we've learned today.  Because our brain has some specific characteristics to remember something, it can't keep all of memory forever. This is the specific characteristic that our brain can keep longer :

1. Senses. We remember things that involve the five senses. Thus, further activate the senses will be easier to remember.
2. Intensity. When there is something more intense funny, sexual, absurd, etc. tend to stand out in our memories.
3. This positions. Problems are boring and unoriginal more difficult to remember because there are problems the ability to distinguish them from all other memories.
4. Emotional - the amygdala, similar to a round nut in the center of the brain - acts as a gate keeper, so when something happens that has a high emotional content - positive or negative - the amygdala says, "It's important," and we are more likely to remember it.
5. Survival - the brain tissue to survive. This means that anything that we consider essential to our survival will be remembered more easily. Survival may include, survival emotional, psychological and financial viability.
6. Self-interest - we remember things that naturally interest us and which relates to personal interests.
7. Repetition - the more often we recall the information, the easier to remember if there is demand.
8. The first and last - our brain is easiest to remember things from the beginning and end of each session or lecture.