The cellular environment is highly heterogeneous and facing the constant threat of protein aggregation. The concentration of each protein type is highly controlled. But how is such regulation achieved when there are thousands of proteins and a combinatorial number of possible interactions? With computer simulations and experiments, we show that the protein folding phase diagram depends largely on the fraction of that protein and is rather insensitive to the presence of the other species. Hence, here we demonstrate that proteins are fundamentally solitary, making the regulation control against aggregation a simple linear problem.