Not so true. And Bruce himself was NOT the greatest martial artist some think. As a innovator, talent, actor, teacher he was good. As he never really did stick to any martial art to learn anything other than basics and some intermediate techniques.
You really need to learn only a few strikes and kicks. And just a few techniques. Since strikes alone will not help you in a crisis situation. You need to know how to get out of a few things like chokes, bearhugs, a few grabs. Maybe a couple throws. Since most of the techniques used to get out of these are almost the same or use similar methods. And you definitely need to learn to combine them in a different manner for different situations. This is one reason why many martial arts use forms as a way of teaching how to move from one strike or technique to another. And you do have to train on a regular basis and be aware of your surroundings.
Don't be fooled Bruce did not know it all or understand it all. He was at best as a martial artist as average and he did borrow a lot of his saying an quotes from other philosophers. He was really not a original in his quotes and sayings a lot were recycled older ones.
Nothing will cover every situation or aspect. If you understand basics and learn how to adapt and combine them in different combos and situations than maybe you will have a chance to survive. Remember when you strike someone you still have to follow thru.
Martial arts and the techniques are not written in stone and a absolute. It is a concept and way of life. What you do standing you can do sitting, laying down etc.
In life nothing is certain.