This is a point I've used for all my research.
You may recall that the system I use says to gather up tons of material on anything you are trying to study and then boil these down by repeating data to find the broad areas, narrow these down to repeating patterns, then study and boil these down to underlying principles.
The next step, as you continue to read and study, is to check on your own interest level.
When you find yourself bored through repetition, then move onto another area. You have to keep track of your own learning curve. Once you've gotten the bulk goods of an area, then you should move on.
Now, as a test of this, I write books. This tells me whether I can simply explain the basics of an area to someone else. And it will show up the holes in my own understanding of an area.
Not for the faint-at-heart, however. Just in writing up the materials for book marketing has taken me for some months away from what I love better - researching self-help and philosophy and personal counselling. In such case, you have to keep your eye on that carrot of what you are going to be able to do when you finish...
There is a lot to life. And anyone can learn and perfect their skills in any subject or area.
Boredom and a hum-drum existence are for those who simply cannot and will not use their innate creativity and imagination to get a better life for themselves.
So, when you quit learning, get out - and find another something which can fascinate you.