Proof at the formal level consists essentially of rearranging the content of a given set of quantified statements to give another quantified statement. These statements relate to definitions of formal mathematical concepts, so if certain properties of concepts are given, others are deduced. The logical part of the deduction is just the tip of the iceberg. The part under the water is a hazard for many trying to navigate for the first time. Expert mathematical thinkers use so much more of their experience to choose concepts worth studying, to formulate them in the most productive way and to select likely lines of attack for proof.