Karma finds its doer by instinct

यथा धेनुसहस्त्रेषु वत्सो विन्दति मातरम् ।
तथा पूर्वकृतं कर्म कर्तारं विन्दते ध्रुवम् ।। महाभारत शान्तिपर्व (१८१:१६)
Meaning : Just as a calf finds its mother in a herd of a thousand cows so also past actions (karma) find exactly the one (embodied soul) who has performed it in the previous birth.