When we get tired, focus and decision-making become more difficult. Not to mention minute-to-minute distractions. This is why it's necessary to practice how to refocus.
I've broken refocus into 3 steps so you can have a go-to process when you're tired or distracted.
Step 1. Mindfulness. Recognize and accept that the past is uncontrollable. Consider withholding judgment to accelerate acceptance.
Step 2. Breathing. Direct attention to the breath to anchor the mind in the present moment. This also helps composure in trying times.
Step 3. Optimism. Focus on one controllable action, or the next best thought you can have. This requires a fundamental belief that the future is going to work out.
There are tons of ways to refocus. This happens to work for me.
Get creative. Make it your own.