A good teacher.
What we all hope to find.
Over the years I have had the good fortune to learn from some very good karate teachers. They have all had one thing in common. The unfailing ability to deliver their knowledge in a manner that left me both physically, and mentally stimulated. And more often than not tired, sore, dripping with sweat, and without exception, always wanting more.
If you are fortunate enough to have a very good teacher in your life, never take them for granted. Never assume that if you happen to miss an opportunity to learn from them that another chance will come along. Life is not like that, there simply are no guarantees. So train with them often, learn all that you can, and remember it.
Then in the years to come if you too become a sensei, be a good one. And pass on all you have learnt to those who choose to follow you.
Remember: "Good teachers are often well down the path we too seek to walk."