As an example of how powerful a single person can be, most places in the country are divided into wards and precincts (I am unaware of anyplace that doesn't do this, but, nonetheless, you have my hedge).
These places send delegates to state (and national) conventions. At these conventions, major fucking decisions are made, such as what the official (state) party platform will be, and sometimes, _who can appear at all on the primary ballot_.
In 2012 I participated in the state dem convention. That fall Liz Warren beat Scott Brown. She had no primary. Why?
Because Marisa DeFranco was unable to convince 15% or more of the state delegates to vote for her at the convention. Even though she was a very liberal candidate and by all measures a great woman (I like her very much but did not vote for her at the convention).
Now, in this setting, my individual vote very easily could have swung things. Marisa came in at around 5-6% or so. I could have persuaded others to vote with me. Etc. Point being it was a lot more power than "just voting."
All I had to do to get this power was show up for 20 minutes to a caucus for my neighborhood ward and precint in February. There was free breakfast.
When we talk about Ron Paul's amazing efforts, or tea party power grabs, or the ascendancy of the Christian Right in the 80s and 90s, we are talking about exactly this -- neighbors taking 20-60 minutes out of their Saturday in the spring to go to the temple and flip some fucking tables.
So when people don't vote or participate, I think, why would someone have this attitude when others have _proven_ that 60 minutes of organizing can do so much?
Addendum: make a reminder for yourself right now for the first of next December January February and March to check the party website in your state to see when your caucuses are happening.
Because they don't set the dates until then anyway, and today's enthusiasm will be forgotten by the time the next caucuses roll around. -- Gerrit Betz
Ten Terrible Reasons to not Vote (and two good ones) by Hank Green