The 20/80 Pareto principle, though not specifically focusing on Forex can be applied in your personal and professional life including trading and applying it will make your life and your trading more productive and more efficient than it used to be. Though I'm sure you can find many books related to that principle, you can find the same valuable information on the internet for free without going through 300 to 500 redundant pages. All you have to do is understand the basics that can be summed up in 10 sentences and think about how to apply it in your every day life
I always try not to waste my time reading 500 pages that can be summed up in just one.
Here, You can grasp the whole 20/80 principle with that short book summary from that 2minutebook website which I think is a brilliant idea to go straight to the point and keep you focused