Everyone has their ups and downs. People often forget that animals are the same way. Before beginning any training session, take time to connect and assess where the animal is at mentally before making any demands. Are they distracted or engaged? Are they moving easily or with difficulty and hesitation?  Taking the time to be as mindful as possible about your partner will help you understand and anticipate their reactions as well as make good choices about what activities or requests they might be able to manage. It is true that you, as the trainer, may set forth the agenda, but the animal will always set the start point.