Galaxy clusters are the most massive collapsed and virialized structures in the Universe. They are rare objects with an irresistible gravitational attraction. Infall velocities derived for some massive merging clusters based on observations are in the order of 3000 - 4000 km/sec. There is a debate right now whether these high velocities are real, and if they are, whether the standard LCDM models can explain their occurrence in the observable Universe. I will discuss the difficulties, caveats, and the possible methods we could use to solve this conundrum.