Despite variations in the extent to which each building block position affects overall activity, the general trend is clear: introducing a high P(active) building block in any position increases the probability of forming an active compound. We find that on average combining monosynthons constructively increases P(active) (Figure ). This means that building blocks that are good independently are still good together on average. While this finding is true on the aggregate, we note that we cannot necessarily propose a specific combination of building blocks which includes a high P(active) building block and expect them to form an active compound without considering the chemistry used to form the DEL. For example, the DEL might have used different reactions for linking different categories of building blocks, so that one part of the DEL might contain active building blocks which simply cannot be linked to active building blocks that would require linking via a different reaction. Or, certain building blocks might be hindered from linking due to steric constraints or other reasons -in other words, the linkage is not synthetically accessible. Thus, we raise an important caveat: the results presented are conditional on the fact that a product is and can be formed, i.e. that the product is a result of what we call compatible building blocks.