I've heard this one before, and I've used it myself often enough.
"Sensei, I've had a bad day, so I won't be training too good tonight. I was late for work, and I had a blowout on the freeway, then I had a run-in with the boss, I forgot to do a message for my wife and now I'm tired and grumpy and...."
"So what? You're here now. Get on with your training".
So our victim of circumstance now has to endure a punishing night in the dojo. The purpose of the lesson is to experience the present moment. Who cares what happened today? Who cares what happened 20 seconds ago?
There's an old story about two monks who happen to come across a river. An attractive young lady is having difficulty crossing. One of the monks lifts her up and carries her across the river.
The other monk is horrified. It is against their rules to have any kind of contact with the opposite sex. Several miles down the road the monk decides to confront his rule-breaking colleague.
"Why did you pick up that woman by the river? It's against the rules!" he complained.
The other monk smiled. "I put her down at the other side of the river. Why are you still carrying her?"
When you enter the Dojo, put on your gi and bow make it a silent ceremony to clear your mind of the day's woes. Present yourself properly for training and focus on the moment.
Anyway, I had a bad day today. Went to the wrong venue for a meeting, had a dull day at work, a difficult evening training and now I'm tired and grumpy. OK, time to take a deep breath!