Both, of these births are births in human race. But, there is a big difference between the two. Therefore, lord Krishna says that the karmas of the previous births reflect the fate, destiny or luck of the individual in the subsequent births.
The Main Ideology of Hinduism:-
Salvation of soul is the main theme in Hinduism. The main goal of the individual is to obtain Mukti or Moksha. If a soul becomes free from the misery of taking rebirth, then it is considered a lucky soul. Lord Krishna has counseled Arjun in Bhagwat Gita about the necessity of salvation and he also showed the path for attaining salvation. Some translations of the relevant verses from chapter VI is given below:-
“The unsuccessful yogi, after many, many years of enjoyment on the planets of the pious living entities, is born into a family of righteous people or into a family of rich aristocracy” (Verse 41)
“By virtue of the divine consciousness of the previous life, he automatically becomes attracted to the yogic principles- even without seeking them. Such an inquisitive transcendentalist stands always above the ritualistic principles of the scriptures” (Verse 44)
“And when the yogi engages himself with sincere endeavor in making further progress, being washed of all contaminations, then ultimately, achieving perfection after many, many births of practice, he attains the supreme goal.” (Verse 45)
These quotes from Bhagwat Gita tell us that efforts are necessary for betterment of luck. The 9th house of horoscope stands not only for luck but also for pious deeds, spiritual practices and dharma. Many people say that man is the architect of his own destiny and the three verses of Bhagwat Gita given above also give a message of continuing effort.
If a person gets something by chance, it may just be a fructification of some past deeds of previous lives. Gifts, inheritance, lotteries and similar gains can be explained as methods of such fructification. Losses, debts and miseries may be because of Rinanu-Bandhan (debts of past life).