I agree completely. Let me put it this way, what if you are some never-seen-before stock market god and you are right 95% of the time. Should you invest 90% in any one stock? Nope, because 1 time out of 20 you will still have unfathomable losses that you cannot recover from, and you will be out of the market.
(By the way, the lesson from this post came to me the hard way. Take heed!)