This can be a slow process with each horse progressing at a different rate. Many miles are put into a horse to build up its stamina and wind. Not only is this a physical process but a mental process as well. They have to learn about starting gates, other horses around them, when to exert themselves and when to relax. Due to the young age, some horse s take longer to get into races and some never make it at all.
Injuries can change plans very quickly.
Once the trainer has prepared the horse to the best of its abilities, it can be entered in a race. At that point the trainer often finds particular parts of the horses training that needs further attention. The trainer also must know when the horse has had enough and needs a mental or physical break. Some require more hands-on, rigorous daily workouts while others just need daily maintenance training to stay fit. There are many reasons a jockey or driver can be disqualified.