where the shoe pinches

where the shoe pinches - причина трудностей, проблемы, неудобств

"that's where the shoe pinches" ( know abt hardships or suffering through one's own experience ) this expsession might in some cases sound closer to "знать/узнать почём фунт лиха"; "вот где собака зарыта"
see also [the name of the game]
see also [вот в чём загвоздка]
see also [вот где собака зарыта]