When you grow up, there are de-facto limitations to what is possible. When your parents tell you, as my parents told me and I'll likely tell my little guy, "anything is possible", "you can grow up to be anything you want", it's not that they're lying, it's just that they're using a convenient form of the word, "possible". They are using possible in the sense of "non-zero probability". In that sense, here are some other things that are "possible"; winning the lottery, turning into a toad, getting reasonable technical service from your cable company, etc. These things are "possible" but certainly not likely.
There are drawbacks to the use of this definition. It's easy to see, and we are quick to learn, that it's largely untrue, and if you press anyone over whose lips pass the words, "you can do anything", you will find that they know it isn't true. There are just too many easily accessible contradictions to the rule. (There's even a meme which highlights these discrepancies.) Like knowing we can't fly before we can conceive that Santa isn't real, as kids we understand and internalise the real rules of possibility before we ever begin to revolt against the implications of our parents precepts.
We've all been lied to, but it's largely OK, and I'll be the last to argue that imaginative playfulness is an evil. But, the danger arises when we learn rules that might not be true. I can't become President, I can't escape my past, I can never achieve my dreams; not really. It's the dreamers which make a difference. It sounds disturbingly like a hopeless gambler to argue, 'well, someone will have to be President'. 'Well, someone has to win the lottery.' Still, the lottery is nevertheless a tax for people who are bad a math.
But I believe in innovation, and what is innovation but carving out an area where you do something that people know can't be done. The smart phone, the Internet, open source software, mobile computing; or even entertainment, a la Felicia Day, in which the makers sell directly to their audience. The exciting areas where world changing paradigm shifts are happening, are exactly those areas where people are proving that the impossible... isn't.
What I want to do with my life, is innovate; it's paramount to saying I want to find where the impossible is possible and that, unfortunately, is no small matter.
I don't know what the secret is; I think maybe the secret is that there isn't one and what it takes is faith and patience and perseverance; but the internal voice, the voice of experience, buffeted about by harsh realism, warns that it's probably not wise to hope for too much, or anything at all. Nevertheless, I need to find a balance, and I think the trick to innovation, is to follow your passion in an intentional way to explore the things you don't understand, to grasp opportunity when you see it (no small task), and to let the rest take care of itself; at least I hope it is.