Skepticism.
 

If I had to put a simile with skepticism, I'd say it's the acid that corrodes one of the main pillars of philosophy: the relation between what we perceive and what's actually in front of us.

You might say, "See this book? I can touch it, see it, hear how it falls to the floor, smell the cellulose of its white sheets and even taste them. I think, this book is really here."

But does that mean the book really exist? Is it really there?

Imagine we were in a Matrix-like reality. That would mean we are not actually feeling by any means that book; it'll all be an illusion from the main control computer. How if everything we're living right now, is not actually what we perceive?

Anyway, being practical, I think it's more useful to take for given that what we perceive is real -you wouldn't be doubting whether that bear running to your place with raging eyes actually exists.

A common issue I see come up with discussions like this is: Is something real because it can be perceived, or is it perceived because it is real (sans hallucinations)? Can something exist if it is never perceived? Other than that, I never really cared for the idea that reality is an illusion (ie- the brains in a jar conjecture) because it doesn't really explain much of anything and it tends to create more questions.

Sorry I just had to. :D
You have an extremely in-depth way of looking at life judging by reading this thread. I do agree that what we perceive is real however, it is kind of cool to think the "what if" factor...about if that bear really exists or not...

That's it. Do things exist because we perceive them, or do we perceive them because they exist? That information has to come from somewhere.

The answer depends on who or what we rely: the observer or reality. Of course, we would go for reality to prove what exists; but there is no way to have "just reality": every piece of information you can have from it is processed by only your senses, perspective and way to look at things. So like it or not, you'll have to rely on the observer.

To put it someway, you cannot have just the landscape in front of you: you might see the mountains if you're on the valley, or a great depression if you're on the top. Reality has not changed, but our perceptions do by changing the perspective.

Anywho, I believe contrasting other points of view may help knowing what we actually have in front of us. So two observers, one from the valley and another one from the mountain, can tell what's really there is a height difference.

Also, understanding what makes us see things differently helps, and how. EG we could not take the daltonic's opinion on the color of the sky seriously without knowing what makes them think the sky is red: their daltonism.

It's something that we can't know either way... if it isn't real, then we can't know it, but it's also possible that if everything WAS a simulation, then we wouldn't be questioning it because that wouldn't be within it's parameters.

Hm, I have a relevant video for this.

YouTube - *Quantum Physics* The Reality As You Know It Does Not Exist

If you cant tell its not real. Whats to say that its not?

We are such stuff as dreams are made on - Shakespeare

It's all about believing what you want to believe, though thinking this reality is not a Truman Show or something Matrix-like will keep your marbles.

I would question reality only if I have experienced something that does not fit in the schemes I had regarding it before.

The question here is by whom... and why.

In response to the title:

Skepticism
The spice of life!

I had to. Forgive my randomness.