The Buddha didn’t borrow the doctrine of karma from anyone. Many people had many theories of karma at the time. He based it on what he saw for himself. Now whether you have faith in what he saw is a matter of your faith in the Buddha- his wisdom and his good-will.
"When the mind was thus concentrated… & attained to imperturbability, I directed it to the knowledge of the passing away & reappearance of beings. I saw — by means of the divine eye, purified & surpassing the human — beings passing away & re-appearing, and I discerned how they are inferior & superior, beautiful & ugly, fortunate & unfortunate in accordance with their kamma: ‘These beings — who were endowed with bad conduct of body, speech & mind, who reviled the Noble Ones, held wrong views and undertook actions under the influence of wrong views — with the break-up of the body, after death, have re-appeared in the plane of deprivation, the bad destination, the lower realms, in hell. But these beings — who were endowed with good conduct of body, speech, & mind, who did not revile the Noble Ones, who held right views and undertook actions under the influence of right views — with the break-up of the body, after death, have re-appeared in the good destinations, in the heavenly world.’ Thus — by means of the divine eye, purified & surpassing the human — I saw beings passing away & re-appearing, and I discerned how they are inferior & superior, beautiful & ugly, fortunate & unfortunate in accordance with their kamma.
[quote=“James, post:27, topic:5834”]
Because you are implying one had to acquire accurate understanding , but who can really determine accuracy of it?[/quote]
No. I meant only that questions like, “How do I know this tree is a tree? And how do I know that I know?” have never much interested me. So it’s better that you raise them with somebody else.
The station of an individual’s birth is decided by kamma, but we can’t assume that everything that happens in our lives is already pre-determined by past kamma. Such a fatalistic outlook would make any effort pointless and futile and would also allow someone to engage in unskillful actions - this is the Buddha’s main objection in AN 3.61.
Regarding your other question about knowledge, maybe you’ll find Mahavedalla Sutta interesting. Some snippets:
Hi Sujith , thanks for your reply .
What i am saying is , we accepted
something we are not sure in the
first place , and , we are really
considering ourselves being
" rational " , " logical " ,
but it is a belief until it’s proven .
Nevertheless , I am sure by
understanding so , still not
causing ourselves in
being " hopeless " .