There are a couple of schools of thought which sometimes clash in forum discussions.
The first is often expressed through the Bruce Lee quote "
Absorb what is useful, discard what is not, add what is uniquely your own." The idea is that you don't have to take everything from a martial art as is. You can use the pieces that work for you as part of your own individual system.
The opposing view is that a martial art is an integrated system of inter-related principles, techniques, and training methods which are designed to work together. Picking a piece out in isolation doesn't make sense. A common metaphor to express this idea is to talk about the absurdity of designing a car by taking the engine from a race car in the chassis of a subcompact with the wheels of a semi, the bumpers of a SUV, the flat bed of a pickup, and the armor plating of a presidential limousine. You get a Frankenstein mis-mash of random parts which were not meant to work together.
I'll set aside for now the JKD response that the pieces selected from different arts are not chosen at random, rather they are chosen because they fit the principles of JKD (or the individuals expression thereof). Instead I'd like to extend the automotive metaphor further.
When I delve into another martial art, it's not because I want to assemble my own system
one piece at a time. I'm more like a design engineer at Honda taking apart the newest offering from Volkswagen to see what the competition is up to and what I could learn from it. I'm not going to just take out the carburetor and stick it in our newest model. I'm going to look at all the tradeoffs the VW engineers regarding power vs efficiency, cost vs safety, use of space, quality of components, and so on. Maybe I'll find an idea I can steal directly. Maybe it will open my mind to new design possibilities in general ("we've always put part A on top of part B, but VW has them reversed. I wonder what other configurations will work ..."). Maybe I'll find a general concept which I can apply to our own designs. Maybe it will just be a good mental exercise in understanding engineering at a deeper level which will improve my own designs in the future.
I've been studying Wing Tsun for a bit over a year now, and I've already started integrating certain WT concepts into my own sparring outside WT class. I'm not trying to become a WT specialist, but I'm also not trying to just pick and choose random cool looking techniques from the art. I'm trying to learn the whole art well enough to understand
why it works the way that it does. Some of my best discoveries have come from saying "
hmmm .. according to everything else I've learned, this is a seriously flawed way of doing things. Why would they do it this way?" and then tracking down the answers. When I understand the concepts behind how things work, then I can understand how and when and if I can apply those concepts to my own art.
We talk sometimes about the different principles of different arts, but ultimately anything that works comes down to the same bottom line principles. The engineers at Ford, Honda, Volkswagen, Rolls Royce, Tesla, etc. all have to deal with the same laws of physics, the same laws of material sciences, the same laws of economics. They're just applying those laws in different ways depending on the intended purpose and market for their vehicles. Same thing applies to martial arts. We all are operating under the same laws of physics and biology. Different arts just apply those laws (some more effectively than others) in different ways according to the context for which they were designed.