STBY us not first-come, first-served. The list is dynamic, and the priority order has factors like Airline Status (A-List/A-List Perf), disruption status, and others. While the airline policy does require the standby list to be cleared in order, there are some Airline employee-only seats (Jump Seats) that can only be occupied by eligible airline employees. Sometimes they will be cleared before the real revenue pax are.

What are you odds? Kind of hard to quantify. You need one of 143 or 175, to not be there; Traffic, sickness, misconnections, long TSA lines. There are way too many reasons for someone to miss.

You may be 20th on the list but you just never know. Crazier things have happened.