That thing you do

I was recently thinking about why people do the things they do, and it occurred to me that the reasons are not too many. I could think of the following as possible causes for people to act at all:

1. The thought that what they do will give them happiness
2. The thought that what they do will give somebody else happiness (this is actually not entirely true, and I'll come back to it in a moment)
3. The thought that what they do will give others pain. Sadists you may identify with this ;-) Actually, this also points back to 1 above, because the deeper motive for causing hurt to others is a (wrong) notion that that will give them happiness.

The more I think about it, the more I'm convinced that there can be no more significant reasons than our own happiness that impels us to act in this world; reasons 2 and 3 mentioned above are really only special instances of reason 1.