Although companies manage project portfolios concordantly with project portfolio theory, they may experience problems in the form of delayed projects, resource struggles, stress, and a lack of overview. Based on a research project compromised of 128 in-depth interviews in 30 companies, we propose that a key reason why companies do not do well in relation to project portfolio management (PPM) is that PPM often only covers a subset of on-going projects, while projects that are not subject to PPM tie up resources that initially were dedicated to PPM projects. We address and discuss the dilemma of wanting to include all projects in PPM, and aiming at keeping the resource and cognitive burden of doing PPM at a reasonable level.