Training doesn't always go smoothly. A dog may start offering random behaviors, stop taking treats normally, vocalize, wander away, or become physically overexcited.
Those aren't just annoyances. They're useful feedback.
Difficulty may be too high
If a dog repeatedly fails a task, the answer isn't always more repetition. The behavior may need to be broken into smaller pieces, the environment may need to be quieter, or the reward may need to change.
Reset instead of pushing through
Take a brief break. Let the dog sniff, move, or rest. Then return to something easy that they already know.
A simple success can restore momentum and give you information about where the difficulty became too high.
Good sessions don't have to be perfect
Training is a series of experiments. Some sessions tell you what works; others tell you that a setup needs changing.
Ending before frustration becomes the dominant experience helps keep training enjoyable and gives you a better starting point for the next session.