Sankaracarya's Vivekachudamani 448

सुखाद्यनुभवो यावत्तावत्प्रारब्धमिष्यते ।

फलोदयः क्रियापूर्वो निष्क्रियो न हि कुत्रचित् ॥

sukhādyanubhavo yāvattāvatprārabdhamiṣyate |

phalodayaḥ kriyāpūrvo niṣkriyo na hi kutracit ||

(Sankaracarya's Vivekachudamani 448)

As long as there is the experience of happiness etc., the work of prarabdha* is seen to persist. Every result is seen to have a preceding action; there can be no result independent of action.

*past actions that have begun in the present life to fructify or to bear fruit.

Sripad Sankaracarya is explaining that all our happiness and sorrows in this world have a connection with our past karma. It's also true that by living today we create karma for the future. By surrendering to the Lord and become his devotee, we can try to understand nullify or reduce our karmas. Everything depends on our willingness.