Surah Najm Ayat 39 and concept of Isaale Thawaab

AsalaamuAlaikum

How would you respond to someone who says that the ayat of Surah Najm mentioned below negates the concept of Isaale Thawaab as it is proof that man only gets that which he did?

The ayat:

وَ اَنۡ لَّیۡسَ لِلْاِنۡسَانِ اِلَّا مَا سَعٰی

And man does not deserve but the reward of his own actions