Quota places, not entries
In most sports the Olympic field is capped, so qualification is a competition for a fixed number of places rather than an open entry list. The place is usually won by the country, not the individual: a nation that earns two spots in a weight category or a boat class then decides internally who occupies them, under selection rules published by its own federation.
This is the single most misunderstood part of the process. An athlete can beat the eventual champion during the qualifying period and still miss the Games because a compatriot was chosen, or because their country never won a place at all. It is a design choice: without caps, the largest and best-funded nations would fill every heat.
The routes in
Athletics and swimming lean on entry standards plus a ranking fallback: hit a published time or mark inside the qualifying window and you are eligible, and if the field is not full, the highest-ranked remaining athletes are added until it is. Combat sports and many team sports run dedicated qualifying tournaments, sometimes continental and sometimes a final global event that hands out the last places. Sports with a season-long circuit, such as cycling disciplines and several judged sports, use their own world ranking as the qualifying instrument.
Continental quotas run alongside these routes to guarantee representation from every region, and a small number of universality places exist so that nations without a qualified athlete can still enter. Host nations typically receive places in team sports, because an Olympics with no home team in the arena is a poor event for the city that paid for it.
Because these routes coexist, two athletes in the same stadium can have arrived by completely different logic — one by clearing a standard, one by winning a regional tournament, one by ranking. Comparing their form before the Games is therefore harder than a start list makes it look.
Selection is its own contest
Once a country holds places, national selection begins, and it is not always a straight time trial. Some federations run a hard trial where the finishing order decides the team. Others reserve discretion for injury, head-to-head record or an athlete's record at previous championships. Both approaches produce appeals, and the appeals are heard nationally rather than by the international federation.
For anyone following the build-up, this means two separate questions have to be answered before a name is confirmed: did the country win the place, and did this athlete win the selection. Reporting that answers only the first regularly turns out to be wrong.
It also means the strongest field in the world does not necessarily appear at the Games, and that is a structural feature rather than a failure. The Olympics is a global event with representational constraints attached, and the medal is awarded inside those constraints.