First if you are training or learning JKD: Bruce said you have to test yourself and techniques in SPARRING....if your FAT...you can't do this! Please dont argue this point! Now I think he can lecture you on a philosophical level and you can learning it...but you will not be doing JKD!
But the whole technician crap....read below.
This is from a question asked of Matt Thornton:
What about those that say you can be a good technician without necessarily being a good fighter.
Think about it... how can you be a good technician if you can't fight? It doesn't make any sense. You don't say... hey that guy is a good boxing technician... but when he spars he just gets mauled everytime. Or that wrestler is a good technician, but his takedowns suck... or that Brazilian Jiu-Jitsu guy is a good technician, but he cant fight on the ground at all. If you said that you would sound insane. But people say that in JKD all the time. Its another in a long line of myths.
You can be a tough fighter without being technical, due to aggresion, size, explosiveness, strength, etc. But you cannot be a good technician without being able to fight, its impossible.
Its similar to when people tell me they think I have taken the Art out of Martial Arts... that its all about fighting only with us... I reply, Art of what?
The Art is in the performance, the doing. Art is in the performance, sharing, and experience of the training itself.
Also, anyone can be a fighter. A good coach can show anyone of even moderate to low athletic ability and intelligence what it takes to become a good fighter. Now, not everyone may then want, or need, to make the sacrifices necessary to get to that level of performance.