What is solipsism about?
Don't worry, it is quite simple. There are basically three philosophic tendencies that carry the name solipsism. To cut a long (very long) story short I will try to describe the "reality/metaphysical solipsism" or "subjective idealism" meant in this campaign (as opposed to "egoism" and "knowledge / epistemological solipsism") in my own, simple words. I am not a philosopher and it's actually quite easy for anyone to comprehend.
Solipsism states that "reality" - e.g., the sky, air, colors, this computer screen, the people walking around - are just a projection of the mind that experiences it, or: self is the whole of reality; only I exist.
The human mind has no valid ground for believing in the existence of anything but itself. There is no independent existence of an external material world, nothing but the self exists. The things of my environment, including other minds, are merely inventions of my conscience. Conscience is my conscience.
From a personal point of view, the universe for you only exists because you experience it. For you, it exists because YOU exist. If you're dead (blackness as a poor metaphor for the absence of ANY sensoric input) it will not exist for you anymore; the universe might still be there, but you couldn't tell, it doesn't exist for you anymore. Therefore, subjectively, the universe only exists because YOU exist. From there, it is only a small step to realize (or "wrongly assume", if you're not a solipsist) that the universe only exists in your mind / imagination.
Now, some of you will say (to coin it colloquially) "hey, if this is *my* universe, how come it sucks so bad?"; the answer to that is simple. Just because it only exists in your imagination doesn't mean that this projection of your mind has to be a pleasant one and/or could be intentionally completely controlled/molded/modified by you, just like you are unable to intentionally/consciously control/change/influence your dreams. You might have a good, pleasant dream or you might dream a nightmare, either way, it is uncontrollable yet it is still _your_ dream, noone else has it.
(Maybe you, like me, as a child have often wondered wether I am not just merely dreaming everything (and I was afraid what would happen when I woke up...). Well, this is a basic form of solipsism, I gave it the term "Lebenstraum" or "LifeDream". Later I found out that Descartes, too, alleged that reality was a "dream", "inventions of my mind" (although in effect he contradicted that). The term "LifeDream" shall henceforth be used here as a way to roughly describe solipsism, it is a familiar term we can work with, but we have to keep in mind that it is not the exactly same sensation normally associated with the expression "dream".)
Solipsism: the world is yours
A solipsist does not try to define reality - he accepts it as his world. A solipsist can not be argued with, since everything you are telling him he believes he is more or less telling himself. You are, after all, just existing in his imagination. This does not, however, mean, that this LifeDream is always pleasant or that you can't influence it. It does not mean you should not / could not for example help a person in need or behave at all in a certain way. That is your way to take influence on your dream...Things do happen in this LifeDream, you can still help a needy person and feel good about something or experience pain.
Solipsism - a philosophical drug ?!
The facts above are not just strikingly logical but also have large consequences. One could argue that solipsism is a good excuse for arrogance. But this ignores the basic aim, no, wrong word, principle of solipsism. If at all it is a very subtle and hardly attackable nuance of arrogance as an unintended side effect of solipsism.
But it has great other potential. If you feel mistreated, your job is lousy, your relationship is a mess, people are annoying you all day, or a certain event or your life in general is a hassle - just remember, it is all yours, it is your dream, it all exists only in your imagination, your LifeDream; if it wasn't for you, none of it would exist. Solipsism is true solace, better than any drug.
But it is also a very dangerous idea. If one gets too indulged into it he might get carried away. If taken very serious and if you believe in it and think about it too much, the effects are just like other drugs.
Sure, there are many who disagree with the idea of solipsism, and they have good arguments, too. But even if one plays a little with the idea but generally rejects it he has to agree that in everyday life there can occur solipsistic everyday effects. Again and again you might ask yourself: what is wrong here?. ..am I the only sentient being here? Are these people really existing? Does anything really exist? Am I the only one to notice something?