I understand your argument that one vote doesn't make a difference, but the whole point of democracy is that we add our ones together. We go into that booth trusting that others will vote the same way as us, and many of us will spend time knocking on doors, or posting leaflets, trying to make sure that happens.It's not depressing it's the truth and you are being dishonest or are failing to see the point.
You said one vote rarely makes a difference, this is wrong in terms of general elections one vote NEVER makes a difference.
I will try again as some seem to be getting confused, I believe when you vote which only you know how you voted you should vote for what you believe. This is the exact opposite of what you are thinking. You have no control over anyone else and the next day the result will be the same.
This is about the individual doing the right thing morally for themselves.
My view is that an individual should do the right thing morally for society, rather than themselves. It's telling that you suggested your way is the only route to being allowed to "complain", which again seems a very individualistic outlook on life.
ps. I said rarely, because occasionally one vote is the literal difference, with some elections being decided on a coin toss.