You don't need to change the world like Bill Gates or Thomas Edison.
Sergey Brin and Larry Page didn't set out to make Google the super success that it was. If it had happened another way, they could have just been a division of Excite.
Bill Gates wanted to have a business advantage but he too never imagined Microsoft to be as large as it is now.
There is success and there is huge success. I think that huge success is more a matter of the right circumstances and decisions turning your way. But reasonable success, I believe, is about good stewardship. If you have reasonable success, then you will be ready when huge success comes to you.
The point is, you can't aim to be a Google or a Microsoft. You have to aim to be faithful in serving customers profitably and coming up with a great product or service. You can aim big, you can aim to be a global leader. But success still comes from the Lord. That's because we don't know what's around the corner.
If only Apple knew that the key to success was actually licensing it's OS, then 95% of us may be using Apple computers today. If only failed search engines knew that the key wasn't going the portal way, but in better search and in directed ads, we may not calling Internet Search "Googling" but maybe "Excite-ing" or "Infosearch". These are the random decisions that could have shaped the landscape tremendously.
The day that Google IPO'ed was just another day for Larry and Sergey. They walked into the same office, and they're overnight billionaires. So what? That wasn't their goal. They were already doing what they liked doing.
I think that a reasonable business goal for a startup is perhaps a 1 to 5 million dollars (by today's standards. That's like selling $200 products to 5000 to 25,000 customers). For hugely wild success, a lot depends on circumstances and taking advantage of opportunities. Do what you like to do most of all.
Aiming high is good but overreaching your ability is also unwise. Take each day as it comes, yet plan for tomorrow and the years to come.