The big question is can you live without kidney? I guess the answer is NO so therefore Bitcoin is the kidney of digital currencies.
Heart would've been a better analogy. Every human has two kidneys but just one heart. One kidney can be taken out if it goes very bad and no replacement made of it and the human will survive but that can't be tried with the heart. Anyway, I catch your drift there.
That's why all the other coins or tokens follow the Bitcoin price thread.
It doesn't always happen that way. You will be safe to say most follow it but it becomes a hasty generalization when you say, "all"