I might need to explain my meaning a little more clearly.
Firstly, 2 + 2=4 is a logical principle. It's a bad example to use since it's not exactly related to evidence-based knowledge. We don't get to the conclusion that 2 + 2=4 by collecting statistics and examining evidence: we don't try putting together two pairs of bricks, two pairs of horses etc. just to ensure that the principle remains invariably firm. Due to our understanding of number, when two and two are placed together, it logically follows that the sum total is four, and anything to the contrary is simply inconceivable.
My comment was based upon how we interact with reality, and how these interactions can contribute to the all-important goal of human happiness. (Because, really, what're we doing if not pursuing happiness?) I think it's indisputable that humankind has advanced tremendously, from a technological perspective, over the past few centuries. But it can still be argued that, spiritually, morally, and psychologically, we're still very primitive. Many of us follow religions that were first adapted to the deserts of ancient Palestine.
The reason why we perform a leap of faith in embracing evidence-based knowledge is this: we assume that a certain arrangement of objects, under the same circumstances, will always behave in the same way. We believe that the Earth will continue orbiting the sun. We believe that our hand will continue to respond to gravity. However, we don't know if these universal laws will continue unwaveringly into the future. I don't know for certain if the sun will rise tomorrow. The sun could have its movement intercepted by some other stellar object; the sun could explode; but, more interestingly, the laws of motion could cease entirely, and the universe could descend into a state where the rising of the sun is as unintelligible as 2 + 2=5.
Some amount of faith and superstition is necessary in order to harbour some form of knowledge. What we need to determine, is how much faith and superstition can result in the best form of knowledge; that is, knowledge which best advances our happiness and tranquility.