Want to make a mark?
Focus on energy production and storage!
Want to make a mark?
Think about generation ships!
Want to make a mark?
Design a way to reform government!
Mankind does not need another social Web site.
The truth that every entrepreneur has to face is that it takes big resources to pursue big ideas, and very few people have big resources at their disposal. Even Elon Musk had to blow up PayPal before he could pursue truly big ideas.
The vast majority of giant corporations come from executing well on a series of progressively larger operational goals. The trick is figuring out how much you can actually bite off successfully at each stage, and then doing it several times in a row and scaling accordingly. The big ideas can come when you have the money and the influence to execute on them.
There is a difference between something that may lead from here to there and something that is definitely never going to lead anywhere.
An example of the former: You write some software that re-orients an array of solar panels to make the most of weather conditions in real time. It's not going to crack the "energy production and storage" enigma, but it's a step in the right direction. Next, you may want to study how panel geometry influences energy collection.
An example of the latter: You set up a Web site that allows teenagers to compare their gadgets.
What big problem are you solving?
And it shows that "important" and "big" work is being done by companies that just aren't on the HN startup radar because, well, it is a different sector. I think people in the internet sector make facebook-things rather than antimalarials because they are in the internet sector.