Karmā:phala (fruit of Karma) is endured by a Jīva (soul) in the form of Puńya and Pápam, and the notion of good and bad will be addressed in this topic. The endurance of Puńya or Pápa by a Jīva in a given lifespan is the Prarabdha. That which is brought upon oneself by actions in past lives that triggered the current existence is known as Prarābdha Karmā. While enduring the Karmā:phala of previous lives, a being performs various actions (kriya) in the current life, with choices made under the influence of the past Karmā:phala. Because of this, a Jīva again accumulates certain karmā in the current life, which is called the Kriyamana Karmā (kriyamana:karmā). Some of this may be worked off immediately, and the remaining – that is yet to be worked off either in this life or in future lives – is called Agami Karmā. The karmā being carried over by the Jīva to various future lives to experience its phala (fruit) results in a loop. The sum total of karmā accumulated by a Jīva from its previous lives to date is called Sañcita Karmā (Sanchita meaning accumulated total). It is because of this karmā that a Jīva keeps taking birth in order to shed it, but with current actions keeps accumulating more. So how does one break the cycle of karmā? This can be explored in the articles of Puńya & Pápam and Kama.
Long answer short: The result of Karma is experienced in a payment plan, not a one shot pay not. Where will there be time for introspection or realization to happen? Most of karma is done out of ignorance or lack of proper understanding or remnants of prior karma preventing them strive toward the realization. But this doesn't mean that Karma's result will always be next life. Its distributed. Why? This is a cosmic concept not a man made concept. All conscious beings invariable strive towards higher states of being, some do so using inquisition, some through surrender, some thought service, and some through desire and the last approach using desire is the longest and hardest way toward that. The force that pulls all conscious beings towards higher and higher states .. this nature/property of cosmos is the eternal property which we call Sanatana (Eternal) Dharma (property).
Source: Karma Link