the concept that you are either alone in the world, and everything around you is a dream of your own creation, or, that as an entity/conciousness, you are completely cut off from everything other than your own perception of things which is fundamentally different than and alien to any other perception of entity in the world and that no1 can ever understand anything outside themselves. it also means that no1 can truly be sure that anything outside of one's own imagination has any existance or meaning.
Can't be proved, is highly unlikely, but can't be disproved and has logic behind it.
end.
__________________ "Life... is strength. That is not to be contested; it seems logical enough. You live; you affect your world. But is it what you want? You are... different inside. This woman lives and has strength of a sort. She lost her parents to plague, her husband to war, but she persevered. Her farm prospered, her children are well-fed, and her name respected throughout her land. She lived as she thought she should. And now she is dead. Her land will be divided, her children will move on, and she will be forgotten. She lived a good life, but she had no real power; she was a slave to death." -Irenicus
Am I all that is? Or are there others, and each of us in an inescapable perceptual bubble? To start here (especially the latter) and muse about reality can be sound, I think, if it keeps one on his/her philosophical toes about their musings and conclusions. But solipsism is not the best "as if" to adopt if it leads to inaction, selfishness or dangerous behavior.
__________________
Shinier than a speeding bullet.