This is not a complete sentence. In order for me, or someone else to help you, we are going to need more context. Where did you see the sentence? What other sentences were around it? The sentence needs another clause. For example, it might be that the sentence goes something like "We make the assumption that simply because we're dealing with a problem, there must be a solution." Without context it's impossible to say. The sentence is incomplete. The phrase "that simply because" has a literal meaning. It means there is an easy to understand or simple reason for something.