Triples that become dynamical unstable during their evolution are born in a specific area of phase space close to the stability limit. The right lower part of the figure is empty as this is the ‘forbidden’ region of dynamically unstable systems. The different types of triples are colour-coded in the same way as in Fig. 2. Black small dots represent triples that did not become dynamically unstable (see Toonen et al. 2020 for their evolution). The x- and y-axes show the initial distance the inner and outer orbit would circularise to if tides were efficient.