You're talking about the bit at 3:00, right?
He's referring to the way that bad/beginner players tend to put a lot of money in on the early streets when their hand is weak, but GTO play is actually quite passive with mid-strength/weak hands. It kind of goes back to the old saying "big hand big pot, small hand small pot". Bad players often pile too much money in on the flop, and then end up playing big pots with small hands.
The recent thread about c-betting A5 on AK6 was a decent example. Bad players that always c-bet their weak aces on the flop will find that the pot is way too big for the strength of their hand if villain is still around on the river. By checking back the flop, the pot stays small, and then A5 is more likely to win at showdown. Newbies are often obsessed with "protecting" their hands, but top pair (especially top pair of aces) doesn't need much protecting, because villain usually only has a few outs. If you make a
big bet on the flop, villain only continues with hands that have a strong chance of sucking out... or are already ahead.