Patañjali's Yogasūtra I.11

I.11 - anubhūta-viṣaya-asaṁpramoṣaḥ smṛtiḥ

Memory is the recollection of a past experience[s].

All experiences leave an impression in us and are stored as memory. It is not easy to decipher if a particular memory is true, false, incomplete or imaginary, as each one will experience the same event in different ways. 

All and each of the five activities of the mind confirm the existence of the mind. They are interrelated and complex. Hence, apart from perhaps sleep, the others should be considered as a matrix of activity rather than as distinct entities. Each of the five can be both beneficial or hurtful, depending on different circumstances. Their consequences may also be either direct or indirect, and maybe seen either immediately or later.