Occasional doubt in Buddhist Teachings

Abhidhamma is the answer for doubting person (vicikicchā-mind-factor just arise with pure moha-mind).

Commentary said that in 3 pitaka:

1. Vinaya-pitaka is for alobha-meditation.
2. Sutta-pitaka is for adosa-meditation.
3. Abhidhamma-pitaka is for amoha-meditation.

Why?

One must leaves every lay's asset, lobha's object, for observing vinaya in vinaya-pitaka. So, vinaya-pitaka is for alobha-development (ordinate to observe monk's sīla).

One must leaves every kāma-loka's senses by jhāna, for living like bhrahmma-deva, like anāgami done. Kāma-loka's senses are causes of dosa, too. Therefore anagāmi, who abadoned paṭiga-anusaya (dosa), abandoned next life in kāma-loka, too. And sutta is very less description, very short, and very less question, when compare with abhidhamma, because buddha taught sutta for the listeners who had experiences in upacāra-jhāna, appanā-jhāna, or upacāra-jhāna-like (ditthi-caritta [uggaṭitaññu & vipacitaññu]). Samahitam cittam yathabhutam pajanati (Good concentrating practitioner will see the truth). So, suttanta-pitaka is for adosa-development (concentration-meditation).

Buddha taught abhidhamma to sāriputta very long description and sāriputta taught paṭisambhidāmagga & niddesa very long description, too. Also, there are millions questions in those canons. Because buddha and sāriputta taught abhidhamma-pitaka for the listeners who have a ton of questions, low concentrating in meditation object, and too much doubts. So, abhidhamma-pitaka is for amoha-development (wisdom/understand-meditation).

So, if you want the answers for every doubts, full-course abhidhamma-study is required by your doubt. Everything in abhidhamma must can analysis their own reasons (causes and effects). So, your doubts can not doubt anymore, after you understand throughout abhidhamma.

I was born into a vietnamese family, so buddhism was a natural part of my life. Maybe it's due to karma I was reborn into my situation, meaning I maybe believed in my past life, so was reborn into a situation where the belief was present?

As for you, I don't know. I am a Theravada Buddhist these past years (different from the Mahayana Buddhism upbringing of mine). You could try visiting buddhist temples of non-Theravadan lineage -- like Vietnamese Mahayanist temples -- just to experience it, and maybe even learn meditation from them (I suggest learning breathing meditation from them). The experience in the Mahayana temples may make you happy, maybe give you faith in Buddhism in general; and if you learn breathing meditation -- in your lower abdomen -- from them, that may give you great happiness...

The differences in the teachings between Mahayana Buddhism and Theravada Buddhism can then be worked out. This was what happened to me. It wasn't planned. I went with Theravada Buddhism later. All I've said is one way it could be done, but don't know if it would turn out good enough in the end -- like for me it did. But note again: it was not planned; but what I'm doing is giving you a "plan" based on my life.

Okay, that was just a "plan". Let's get right to Theravada Buddhism. Here is a good book on Theravada Buddhism to maybe help you sort out your doubts:

'Good Question, Good Answer' by Bhante Dhammika

https://www.bhantedhammika.net/good-question-good-answer

It seems like you are afflicted with one of The Five Hindrances called Doubt.

From Gil Fronsdal, we find a description of doubt below, quoted from here, and he differentiates between "hindering doubt" and "questioning doubt".

Doubt as a hindrance is a mental preoccupation involving indecision, uncertainty, and lack of confidence. It causes a person to hesitate, vacillate, and not settle into meditation practice. Its simplest manifestation can be a lack of clarity about the meditation instruction, which may be settled quickly with further instruction. More dramatically, doubt can involve deep, fiery inner conflicts and fears stirred up by the practice. All along the spectrum, doubt can keep the mind agitated, perhaps simmering in discursive thought and feelings of inadequacy. Alternatively it can deflate the mind, robbing it of interest and energy.

“Hindering doubt” is not the same as “questioning doubt.” Doubt as a hindrance leads to inaction and giving up. Questioning doubt inspires action and the impulse to understand. It can, in fact, be helpful for mindfulness practice. A questioning attitude encourages deeper investigation. It is a healthy doubt that can overcome complacency and loosen preconceived ideas.

Hindering doubt takes many forms. It can be doubt in the practice, in the teachings, in one’s teachers, and, most dangerously, in oneself. Doubt may not appear until one is actually beginning to practice. A person may spend months happily anticipating a meditation retreat only, upon arrival, to doubt whether it is the right place, time, or retreat to be on.

Doubt is often accompanied by discursive thinking. Sometimes thoughts can appear reasonable and convincing enough to mask the underlying doubt prompting them. But regardless of whether it is reasonable or not, the discursive thinking can interfere with the meditation practice and so confirm doubts that the practice is not working. In other words, doubt can be self-fulfilling.

If you have questioning doubt regarding the teachings, then you should start investigating deeply.

If you have hindering doubt regarding the teachings, read below and further on the website.

Once hindering doubt is recognized, there are various ways of working with it. Occasionally a period of careful contemplation may resolve the doubt. When doubt involves uncertainty about the practice or the teachings, it is helpful to study, learn and reflect on the Dharma itself. Asking a teacher or having a talk with a dharma friend may also help in this regard. Having a clear understanding of the Buddha’s teachings on what is skillful and what is unskillful can go a long way toward overcoming doubt.

(snipped)

Finally, it can be helpful to remember something that inspires you in the practice, such as a teaching, a person, or some experience you have had in the practice. Bringing this to mind may remind you of why you are doing the practice and how much you value it. It may gladden the heart enough to clear away the clouds of doubt. It may even encourage you to rededicate your efforts to transform everything into your path to freedom, including the hindrances.

Doubts mean that you are looking at the same problem in different angles... isn't' that so. For example,

There can be no right or wrong answers to most of the questions you have and you really have to keep making mistakes and follow the path your heart chooses. Same with the things in Buddhism...

I was and probably still am a skeptical person. A couple of tips: Don't force yourself to believe in anything (especially far reaching goals like enlightenment and rebirt etc because you cannot prove them to yourself). Rather, test the teaching out step by step and do not digest to much teachings at once. Practise certain meditations like loving kindness in a step by step manner and see if you feel better. Read for example the first five or so paragraphs by the dhammapada and look if they make sense and stay there for a couple days or weeks to gain confidence.. make much of them.. cultivate it (bhavana). If doubt arises talk to yourself and remind yourself that everything can be criticised and to seek for the ultimate truth is a waste of time.. if you judge a person is that ultimate truth? No? Is science ultimate truth? No, also constantly changing. And keep in mind that whenever someone criticises something or you do it by yourself you should only allow or regard it if it's 1. constructive and 2. your have a good replacement at hand, otherwise it's a waste of precious time and mentally draining. You could ask yourself for example: What are reall the disadvantages of loving kindness? Almost none. What are the disadvantages (both long and short term) of not meditating, being kind, chasing worldly things.. Isn't the mind causing most suffering? Have an internal dialogue and do so repeatedly. This comes from my own experience.

These moments of doubt is exactly when you are making the choice to be happy or not. If you trust your own hope for the best and go for it, without reluctance, you will progressively arrive at a place when you get enough evidence that it works, and the doubt will melt away. Just don't cling to the pessimistic leg of the ambiguity fork, out of fear.