"A fish can't whistle and neither can I." Coming from a wise mind, such a statement would mean, "I have certain limitations, and I know what they are." Such a mind would act accordingly. There's nothing wrong with not being able to whistle, especially if you're a fish. But there can be lots of things wrong with blindly trying to do what you aren't designed for. Fish don't live in trees, and birds don't spend too much time underwater if they can help it. Unfortunately, some people—who always seem to think they're smarter than fish and birds, somehow—aren't so wise, and end up causing big trouble for themselves and others.
That doesn't mean that we need to stop changing and improving. It just means that we need to recognize What's There. If you face the fact that you have weak muscles, say, then you can do the right things and eventually become strong. But if you ignore What's There and try to lift someone's car out of a ditch, what sort of condition will you be in after a while? And even if you have more muscle than anyone alive, you still can't push over a freight train. The wise know their limitations; the foolish do not.
...A saying from the area of Chinese medicine would be appropriate to mention here: "One disease, long life; no disease, short life." In other words, those who know what's wrong with them and take care of themselves accordingly will tend to live a lot longer than those who consider themselves perfectly healthy and neglect their weaknesses. So, in that sense at least, a Weakness of some sort can do you a big favor, if you acknowledge that it's there. The same goes for one's limitations, whether Tiggers know it or not—and Tiggers usually don't. That's the trouble with Tiggers, you know: they can do everything. Very unhealthy.
Once you face and understand your limitations, you can work with them, instead of having them work against you and get in your way, which is what they do when you ignore them, whether you realize it or not. And then you will find that, in many cases, your limitations can be your strengths.