How is Karma valid ?

Respected Anonymous ji
This is the Karam philosophy. It is very important to understand this. Most of the time we keep interpreting it as we see it fit. But in Gurbani the Hukam is:
ਮਾਥੈ ਜੋ ਧੁਰਿ ਲਿਖਿਆ ਸੁ ਮੇਟਿ ਨ ਸਕੈ ਕੋਇ ॥
This means that Hukam uses Akal Purakh. He, who understands His Hukam, performs deeds according to the Hukam, writes the writing on his forehead according to the deeds he has done. Man cannot escape the consequences of his deeds.
ਨਾਨਕ ਜੋ ਲਿਖਿਆ ਸੋ ਵਰਤਦਾ ਸੋ ਬੂਝੈ ਜਿਸ ਨੋ ਨਦਰਿ ਹੋਇ ॥(1413)
Meaning whatever deeds we have written, God has to reward accordingly. Whoever understands the Hukam of Akal Purakh, then that human being becomes the recipient of His Nadar.
Our result will be the same as what of we write in the paper. If we act according to the Hukam of Akal Purakh, then the inscriptions on the forehead will also be auspiciously written. We have to understand God’s Hukam and do good deeds accordingly.