The problem with that question is the assumption that you can’t.
Thing is, you can change the world. People do it all the time. Sure, being rich or powerful is what most think of--supernaturally powerful in many cases, but that's just impatience.
For example? Need to be a millionaire first? Fine--an astonishingly small amount of money set aside each week in a very conservative no-load mutual fund will generate millions over a normal work life. Most people don't, excuses in place. Yet you'll see stories every so often about a janitor who leaves five million to cancer research--how'd that happen?
Many people then turn to the vote. Yes, that's important--vote. Excuses quickly enter here too--there's no one worth voting for, politicians don't care anyway, it's all about money and so forth. Let's take a look:
No one worth voting for? Both major parties have fielded a dozen candidates of all different factions of their parties. Third parties are alive and well--and some are growing. All of those candidates start with "retail politics," talking to one person at a time. When they can't do this, their supporters do. I once heard an interview with the founders of Greenpeace and Earth Day. They were asked how they got such large movements going from the ground up. they both said the same thing: "talk to one person, then talk to another person, then talk to another person." And hey, you could always make a small donation to your favorite candidate--millions of those small donations mean major campaign funds.
Politicians don't care? Ever write to one? No time? Hell, how long does it take to write a letter? Or an email? People do the equivalent here all the time.. Send one a week, one a month, one a season, one a year--but you'll find (1) you will get a response and (2) they do pay attention--literally add up the pros/cons, etc--your letter marks you as a likely voter. I have even used my elected officials for help resolving business and governmental problems, quite successfully. (I can't call the Comptroller of the Currency about a bank pushing me around inappropriately--but my Senator sure can!).
I've addressed the money issue in part in two different ways already, so let's move on....
The above are some typical ways people think about changing the world. This post is about the ways they overlook.
One person can most definitely change the world. A patent clerk in Switzerland named Albert wonders what it would be like to ride a motorcycle across the universe at the speed of light, and in 1905, publishes a paper--that will in time lead to nuclear weapons and nuclear poser. James Watts wonders if the natural heating and cooling of water could help drive a pump to solve the constant drainage problem he faced--and started the Industrial Revolution. A messy scientist notices his poor housekeeping has spawned a mold--and we get antibiotics. We could go on and on in this vein, of course.
OK, we aren't all scientists--ordinary people sometimes get cool ideas too, from the safety pin (an idea worth millions) to hooking up a circuit board to a television in a garage and starting Apple Computers. But OK, we aren't all inventors either.
How about the twelve-year-old boy who saw a homeless man and organized a blanket drive that generated several thousand blankets distributed? Anyone could have done that. Anyone didn't--he did.
Granted, you can't just wave your hand and the world is magically better. You can just explain to yourself that the problems aren't solvable, that it wouldn't do any good anyway, that really those problems are somehow good or "God's" plan or Nature's plan or any other of the self-serving nonsense people use to justify doing nothing.
But bit by bit? An improvement here or there? By looking for solutions instead of complaining about problems? With a little patience?
Absolutely. One person can change the world--the only prerequisite is wanting to do so and taking action instead of creating excuses. Maybe start with just changing parts of it.