"It just seems obvious to me that sensation isn't always there. I get an itch and then it's gone. I have a pain and then it's gone etc etc. maybe I'm misunderstanding this concept??"
Yes, it's as ordinary as you put.
"Does it mean that for example an itch that lasts for 10 seconds is not continuous for the 10 second duration?"
You can refine the observation as much as you are able to and observe differences in the itch during these 10 seconds. A crucial point in these observations is that it's not stable: "it" mutates (impermanence). A second crucial point is that it doesn't seem proper to regard "it" as a substance, because scrutinizing it fails to uncover that "it", that substance. What is there is an on going process changing over time. Any substance we find there, upon scrutiny, is shown to be, ultimately, another underlying process.
"And same with a pain? Perhaps my concentration is not strong enough to ever notice this. I try to examine a sensation sometimes but an itch just seems like an itch to me."
Some people, unable to make it go away, may come to think an itch is something that can be there forever. Some other people may think an itch is an act of spirits. Other people may think that an itch is something that knows you did something bad in the past and is punishing you. This variety might illustrate the kind of people that was exposed to this practice. Then, the practice would help these people see what you just said without the added color and imagination (it's but an itching) but also get in touch with it's workings and real nature.
It get's interesting when instead of itch, we are talking about anger...or even love. Aspirations, fears and desires, things we dislike and so on. Of course, more so if the subject of investigation is ourselves.
"Sitting, noticing breath, thinking, noticing breath, itch, thinking, notice breath etc. It feels more and more pointless everyday. I don't seem to be learning to see the "true nature of reality" or heading toward "enlightenment" Why not? Where am I going wrong?"
The development of this practice (in particular, associated with mindfulness of breathing), when correctly exercised, has a few benefits such as:
- We get undistracted and alert (it prevents proliferations of thoughts).
He should develop mindfulness of in-&-out breathing so as to cut off distractive thinking.
-- AN 9.1
- In general, we get calmer and the faculty of concentration is unobstructed (so we can develop it further).
"Contemplating foulness in the body,
Being mindful of in-and-out breathing,
Ever ardent and seeing clearly .
The calming down of all formations"
-- Iti 85
"For one of right mindfulness, right concentration springs up."
-- SN 45.51
"Bhikkhus, being alert and mindful, develop concentration that is measureless."
-- AN 5.27
There are, bhikkhus, forms cognizable by the eye that are agreeable and those that are disagreeable. One should train so that these do not persist obsessing one’s mind even when they are repeatedly experienced. When the mind is not obsessed, tireless energy is aroused, unmuddled mindfulness is set up, the body becomes tranquil and untroubled, the mind becomes concentrated and one-pointed.
-- AN 4.51
A very important point here is that the practice of concentration is a key pleasing aspect of Buddhism. It's by practicing samatha that we find some protection from undesirable states of mind (anger, frustration, resentfulness, obsessions, etc). It's samatha that envelops us in a kind of pleasure that is beyond the ordinary pleasures of our lives. And it's samatha that gives a taste of the ultimate bliss, Nirvana.
As mindfulness practice calms us and unobstructs concentration, we get in a good position to practice concentration. Then, when concentration gets well developed, it is concentration that unobstructs insight.
All the practices of the eightfold path go hand in hand, they are platforms for each other. They also help explaining each other.
It's important to understand the eightfold path in detail, in order to contextualize what one is doing. It's a map, it gives us direction and means to evaluate where we are. If all we are doing is "mindfulness meditation", it can be hard to know what we should be looking at and what we should be doing or if we are doing something right at all.