When a child is in its your mother's womb, or is a one-year-old, it is not in a fit state to remember anything long term - so whether we like it or not, it actually makes sense that most adults can't remember anything from before a very young age, let alone from before this life. Having said that, there have always been some people who have claimed to remember past lives. Many are children, who may lose such memories before they reach adulthood, while others get spontaneous glimpses into their past because a specific event triggers the memory. Such memories are as mysterious as any other unexplained (or psychic) abilities. Unfortunately such people often keep these memories to themselves - for fear of ridicule. If people are open to the idea, and approach the subject with people in an appropriate way, it can be surprising how many people you do meet who have experienced some kind of past life memory. There are also plenty of books on the subject and some very compelling cases indeed.
Regression therapy is yet another tool to delve into the deepest recesses of our memories and many sceptical hypnotherapists have conceded in the face of mounting evidence.