Writing in a thick notebook can be troublesome when you get close to the end of a page. If you're like most people you will encounter a zone where the palm, fingernails or wrist (which I will refer to collectively as "palm") of your writing hand have nowhere to rest, and you may find yourself trying to "float" your hand over the page. As a result, control of the pen-tip becomes enough of an effort to hamper the free-flow of thoughts from the brain through the nervous system to their final conversion to written word.
At best, you get your point across, but usually not without some effort, frustration, and sloppy penmanship.
I suppose one could simply turn to a fresh page before this becomes an issue. That would probably be ok with cheap notebooks, but if you are reading this, yours is probably not cheap, and you intend to wring out all of its value by using every bit of its space.
Thus, as your palm starts to drift off the bottom edge of the page, it needs somewhere to rest...two possible solutions come to mind...one is free, the other cheap:
1. The Smart Phone Trick (free)
2. The Writing Mat (cheap)
The Smart Phone Trick
Placing your smartphone at the bottom of the book at the right point serves as a rest for your palm. It feels like instant relief, at least compared to the alternative of doing nothing at all. It's as if your hand lost its balance at the edge of the page, and the phone is there to catch it.
A smart phone is also a very good thickness (about 10mm) for this purpose. At some point it will be lower than the page you are writing in, and at other points higher, but the differential will never be very great because you won't always need it.
A thin paperback also works well for this purpose, but it can't be too wide or long because it will use up a lot of desk space and may even dig into your forearm. And you'll have to always remember to have it on hand. So, a smartphone is nearly the perfect size....and it is very handy for many of us most of the time. It may take some trial-and-error to figure out exactly when and where you need to deploy the device, but once you do, you will once again find your thoughts freely flowing to any point on the page.
And, as a pen-and-paper person, you may gain some satisfaction from knowing that technology doesn't always exist just for its own sake.
The Writing Mat
Writing mats (sold on this site) are great for enhancing the pen-to-paper connection, and if while writing you press hard with fine points it will protect the lower pages from impressions.
They are also great as a lower extension of the page you are writing on. For that purpose the thin plastic mats seem to work better than the soft mats because they are stiffer and give more support to the palm. But the soft ones work fine too. As you get to that troublesome point on the page, you just keep moving the mat down as long as you need to, and it provides a gentle slope on which your palm can rest.
The mat should be at least the same size as the paper. It can be larger, but larger doesn't have any real advantage other than being able to work with more notebook sizes. They are also harder to carry around. But even if you have the perfect size mat, you have to remember to have it with you, so you may prefer the smart phone trick anyway.
There are many folks that don't write in notebooks because of this very issue, but given these simple solutions it doesn't have to be hard at all. There is also a certain feeling of satisfaction, security and abundance when writing in a thick notebook, and anyone can deploy these or similar tactics in order to get the full experience.