I'm not sure whether it has been poorly taught by a monk but as far as I know the Buddha never really taught to just merely watch the hindrances, right? The sixth factor of the N8P is right effort and it calls us to do something about the hindrances. But why then does the Buddha at other times say that we have to see the impermanence, the unstability (non self) and the unsatisfactory nature of thoughts, feelings, emotions etc? Should we do both approaches or mainly right effort?
Val, hindrences have to be overcome by right effort and phenomenas, as they really are, can then be observed on a more refined level, a level that is then not so much subject of defilements. Right effort is required to build upon the foundations to errect the whole path and serves as entrance upon the Samadhi section and at the same time connects the other single elements of wheel so that it might beginn to roll for an end of suffering.
"One tries to abandon wrong view & to enter into right view: This is one's right effort...
"One tries to abandon wrong resolve & to enter into right resolve: This is one's right effort...
"One tries to abandon wrong speech & to enter into right speech: This is one's right effort...
"One tries to abandon wrong action & to enter into right action: This is one's right effort...
"One tries to abandon wrong livelihood & to enter into right livelihood: This is one's right effort."
— MN 117
There is no such as right concentration if there is not also the factor of right effort involved:
"Now what, monks, is noble right concentration with its supports & requisite conditions? Any singleness of mind equipped with these seven factors — right view, right resolve, right speech, right action, right livelihood, right effort, & right mindfulness — is called noble right concentration with its supports & requisite conditions."
— MN 117
The single factors are not to be seen as being abound once reaching a certain but as a coming together of all, like the single supports of a wooden wheel.
Of what is finally right effort on even the most subtile levels on knows after the gain of path and fruit.
Just this right effort, in simply ways taught by the Buddha to his son will bring one to the final liberation and to develope all needed factors.
"Exertion is most helpful for the final attainment of the truth, Bharadvaja. If one didn't make an exertion, one wouldn't finally attain the truth. Because one makes an exertion, one finally attains the truth. Therefore, exertion is most helpful for the final attainment of the truth."...
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]
But why then does the Buddha at other times say that we have to see the impermanence, the unstability (non self) and the unsatisfactory nature of thoughts, feelings, emotions etc?
Isn't that "right view"?
And isn't it an antidote to the craving and attachment, which the second noble truth defines as a condition of dukkha?
Should we do both approaches or mainly right effort?
I think that the noble eightfold path (of which "right effort" and "right view" are two) is meant to be all practiced -- not one or the other, but together. Or perhaps successively: I think there are also explanations which say you practice one after the other, or that one leads to (or is related to) another somehow; like when a wheel is rolling, the weight is supported on one spoke then another.
Some definitions say that right view is the primary, that everything else follows from right view: that you have right intention, for example, because or if you right view; or that right view defines what "right" intention is.
Did someone say that the four noble truths is a doctrine taught more to monks than to laypeople, though?
According to a different analysis, the eightfold path can be viewed as the threefold training. According to that classification, I think everyone agrees that virtue is primary or most important, foundational.
There are definitions of "right effort" on this page. Those definitions make it seem to me that that is foundational, perhaps a sine qua non (i.e. a factor without which the other factors don't exist).
To be, or not to be: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them?
So what is the Buddha's teaching? To be, or not to be? In my opinion, Buddha is dubbed "The Victor", not "The Loser", for a reason ;)
As I understand, Siddhartha was on the quest for a permanent solution to death and, generally, life's perpetual troublesomeness. What he found instead was the realization that the universe's very nature is characterized by invariable Impermanence, Dukkha, and Nothing-is-ours-ness. Think about it! He was looking for deathless peace and found Anicca, Dukkha, and Anatta! In some sense he had lost, he'd realized his quest was absolutely and utterly impossible!
As he thus gave up on the quest - or ceased all efforts - I imagine he suddenly and with great surprise realized that his entire drive - the aversion to the world, the longing for Beyond, the hoping for permanent bliss, the suffering of not yet having achieved it - were due to his silly attachment to a set of abstract ideas... The ideas of Self, Permanence, Happiness. The ideas of Victory, of Success, of Transcendental Realization. The idea of Escape... This pain and this longing for That - turned out to be coemergent. This longing and this aversion to This - turned out to be coemergent!
He then realized that attachment to and longing for any idea of "that" and aversion/suffering in regards to "this" are always dependently-coarisen and lead to pain. As he dropped his longing, he dropped his pain.
He discovered that our perception of everything is our own interpretation or projection based on our assumptions and attachments. This means that our hell and our heaven is our own creation. In other words, suffering and happiness are conditional, and therefore can be controlled and manipulated. We can stop suffering and generate our own happiness. Finally, he found that by going beyond all assumptions and attachments, by relinquishing all positions, our experience loses all ground and becomes conditionless - so suffering has nowhere to stand - which makes us immune to all trouble, completely and 100% imperturbable!
So at the end of the day, the resulting suchness - the experience of living in baseless, selfless state of total acceptance and total understanding - does look somewhat similar to simply surrendering to our powerlessness in this uncompromisingly transient, painful, and uncontrollable world. However, by taking control of our mind, of our narrative, of our interpretation, by dropping all attachments and all ground of suffering - we have fooled the ever transient/painfull/uncontrollable world and solved the unsolvable problem!
Now, to directly answer your "to be or not to be" question: "Buddha never really taught to just merely watch the hindrances", "Noble eightfold path includes the right effort and it calls us to do something about the hindrances. But why then does the Buddha at other times say that we have to see the [(hopelessly immutable) Anicca/Dukkha/Anatta]? Should we do both approaches or mainly right effort?"
Correctly seeing Anicca/Dukkha/Anatta is part of The Right Effort. Like I said above, the idea is to skilfully control our attention and our interpretation. My teacher explained it like this: When you completely accept Anicca - you attain the deathless. When you completely accept Dukkha - you attain the painless. When you completely accept Anatta, you attain freedom. When you completely accept Samsara - you attain Nirvana. -- All of this works when you no longer hold on to a certain conceptual ground that coemerges with its negative counterpart.
So it's not really "observe" vs "right effort". They are not in opposition to each other. Observing Anicca/Dukkha/Anatta is right effort. Correctly seeing them in a positive way is called "right attention", or seeing things skilfully.