Brussels South Station (Bruxelles-Midi/Brussels-Zuid) is generally quite a decent modern transport hub, with clear logistics, with all the services passengers need. But here is the Belgian Railways company, for which trains, strictly speaking, this station is needed, full out. I had to use SNCB/NMBS trains a dozen times and they were always late! Always. Both on arrival and on departure, often for more than half an hour. Something like that...
A large train station with difficult logistics. It is worth taking a reserve of 10-15 minutes to calmly figure it out. There were queues at the Eurostar ticket offices, but small ones. I bought tickets on the website.