Verifiability
I urge all editors to read Wikipedia:Verifiability. This is official wikipedia policy. I would like to point out this section in particuluar:
Articles should contain only material that has been published by reputable or credible sources, regardless of whether individual editors regard that material to be true or false. As counter-intuitive as it may seem, the threshold for inclusion in Wikipedia is verifiability, not truth. For that reason, it is vital that editors rely on good sources.