The discussion clarifies why +bc becomes negative in the proof of the Euclidean Algorithm, emphasizing that the expression d/(a-qb) is preferred over d/(a+qb). The reasoning is based on the relationship between d/a and d/bc, which leads to d/(a+bc). It is explained that using a-qb simplifies the equation, allowing for a more manageable calculation. The alternative, a+qb, results in larger numbers, making it less useful for subsequent steps. This highlights the importance of choosing the correct form for effective problem-solving in the algorithm.