Originally Posted by threeoh

My assumption is that WN does not want to IDB/VDB any passengers. Therefore, on a day with no IRROPS, the chance that at least one standby passenger will clear is fairly high. It is not the case that Southwest says "we think there will be 5 noshows, let's overbook by 5" -- they probably say more like "we think there will be 5 noshows, but have 95% confidence there will be at least 2 noshows, let's overbook by 2". Then they will probably get 2-8 noshows, so they will probably clear 0-6 people off the list. Chances are that number is not 0.

Basically one of these five things has to happen for you not to clear the standby list:

(1) someone clears but that someone is not you
(2) you are in a group of more than one person
(3) IRROPS earlier in the day / previous day
(4) a big event leading to high demand (superbowl, eclipse, holiday, etc.)
(5) you're in that 5% (or whatever) risk window where Southwest either has to IDB/VDB someone or comes very close to doing so.

You can see 2, 3, and 4 and make a risk assessment. 1 and 5 come down to a roll of the dice.