Past lives are a matter of belief. Some people are convinced they absolutely are are are not real. Some believe they are a possibility, but there is no real way to prove it, while some believe that the spirit or soul (or whatever, according to belief) maintains some memory. Yet there are some others who believe that the essence, spirit, whatever, of the person returns to the universal energy, from which energy is dispensed for new lives -- and that we are not one spirit each, but a part of a large collective energy. And there are so many other beliefs besides these.
I do not promote one belief above any others. However, the concept of a past life is definitely not a universal concept.