Is it possible for citizens to influence decisions of government and corporations?

Yeah!
What do you think?

That's sort of the point of voting...

I think he means beyond voting, as in having your voice heard.
Im fairly naïve, so I believe that one person can make a difference, there has been small, isolated happenings that have radically changed things, I just can't think of any right now, they are on the tip of my tongue. Some influential individuals would include Civil rights activists, who are beyond the government, but have made a huge difference. Like that femenist chick, steve irwin has made a huge difference recently, having spread huge amounts of awareness for issues to do with thhe environment, and he isn't in the government. So maybe, you can make a difference, you just got to get your voice heard! My personal belief is, as long as you make a difference to one person, you've done a good job.

It happens all the time. People write letters to their elected officials and vote out of office people who don't do what a majority of voters want. Corporations rise and fall based upon the decisions consumers make as to whether to buy their products or services.

Haven't you ever heard an elected oficial cite the fact there had been a great deal of e-mail/phone calls/etc to support or not a particular piece of legislation? Get enough people to complain about a product or the way it's advertised and the comp changes/withdraws/etc. The problem is getting enough folks to actually express their opinion in a way that's heard by the target.