Applications are rarely lost on the strength of the candidate. They are lost on process.
Deadlines and the pieces behind them
The application deadline is not the only date. Test scores have to arrive, teachers have to submit references, and transcripts have to be issued.
Each of those depends on somebody else and each takes time. An application submitted on the last day with a reference still outstanding is not a complete application.
A list built without reading requirements
Course specific requirements exist, particularly in the United Kingdom. A subject that was never taken cannot be added in the final year.
The requirements should be read before subjects are chosen at sixteen, not when the application is written at eighteen.
One essay sent everywhere
Where an institution asks its own question, an answer that could have been written for any institution reads exactly as such.
This is visible immediately and is one of the few things that actively harms an otherwise strong file.
A list with no realistic middle
A list of ten highly selective institutions is not a strategy. Neither is a list where the student would be unhappy at every safe option.
The useful version has genuine range and no entry the student would refuse to attend.
Taking an exam too late
An exam whose results arrive after the deadline has not been taken, as far as that application is concerned.
This is pure arithmetic and it is the mistake that is easiest to prevent and most painful to discover.
Leaving the language requirement to the end
Proficiency exams have their own dates, their own result delays, and validity periods. A score that expired, or that arrives late, blocks an application that was otherwise complete.
The pattern
Almost every item here is administrative and could have been prevented by a calendar written a year earlier.