The problem with suited connectors and especially with small pairs is that their value depends on hitting the board very well. If you have a big stack you could profitably play these speculative hands maybe twenty times in the hope of getting a big payoff once when you make a set or a well concealed straight. These are the implied odds
that Harrington is referring to.
When your stack is lower, you don't have that luxury and simply pairing your middle range card (8 or 9) when you are desperate could be very costly.
You can still play looser with hands that at least have a chance to win — A8-AJ, KT, KJ are not premium opening hands but when you are up against it they could easily become a winning pair.