Boredom means that the teacher has stopped trying.

"but the student is not motivated and never practices..."
The teacher is not powerless against this. If someone is shelling out their hard earned money, there has to be some motivation somewhere. Can the teacher find it?

"the student does not understand anything I say"
Try a different explanation. What works on 90 percent of students may not work on this one.

"the student makes no progress"
Is there really nothing a teacher can do about that?

When a teacher reaches true boredom...ie "they have run out of ideas or they do not wish to invest the time to learn a whole new way of teaching", then it is proof that this particular teacher-student match is not good. It's certainly not the end of the world.

I get bored with students that I can do nothing for. It takes a long time for me to go through all my "bag of tricks". If none of them work, and I reach boredom, I let the student know that I feel they are not getting value for their lesson money.

Having said this, I can remember only 2 cases where this became necessary. Usually in the 2nd or sometimes 7th way of teaching something stuck.