Confronted with problems or situations that do not yield to known theories and world views, the scientists and students are alike. Rarely are they able to directly build a model or a theory thereof. Rather, they must find ways to make sense of the circumstances using their current knowledge and adjusting what needs be in the process. This way of thinking, using past ways of perceiving the physical world to build new ones, does not follow a logical path and cannot be described as theory revision. Likewise, in many situations it is awkward, indeed often impossible, to resort to analogical reasoning to account for it. This paper presents a new mechanism, called 'tunnel effect', that may explain, in part, how scientists and students reason while constructing a new conceptual domain. 'Tunnel effect' is also contrasted with analogical reasoning.