The forgetting function
In this answer about the relationship between time and recall I discussed how research shows that the relationship is often characterised by a three parameter power or exponential function. The basic idea is that the recall is a monotonically decreasing and decelerating function of time since the event.
Forgetting as adaptive behavior
In general, I think that this is an adaptive feature of human memory. More recent events or more frequently recalled events are more likely to be useful to daily functioning.
Many theories (e.g. ACT-R) of cognition assume that cognitive activities come at a cost. Thus, storing information comes at a cost at some neural-biological level. Likewise, storing more information is likely to increase the time of access to that information. In both cases, forgetting more distant information is likely to be adaptive in some sense.
There are wide range of strategies for better recalling information. However, presumably you are not wanting recall all events and all information, but rather information relative to achieving some goal.
Some general strategies:
- rehearsal of the information; or just using the information in some meaningful way
- cognitive elaboration of the information (e.g., exploring relations, adding meaning, giving structure to the information)
One option, of course, is to externalise your memory such as by writing things down, or recording information in some other way.