This applies only if you are a student of a martial art form that practices kata, forms, or something resembling that. The tip is, don't stop practicing an old kata just because you've moved on to learning a new one. In many schools, and definitely where I train, knowing all the katas that have been taught is required. More than once, I've asked a student what kata they are working on, they tell me X and I tell them to do Y kata, one they had done one or two belt promotions previously. The dropped jaws and blank stares are priceless. The kata are taught for a reason, and it's not like algebra which you will never use again in your life once you've passed the course (well, I didn't anyway). The kata contain within them techniques which are obvious and explained (usually) and many more which you will have to become much more proficient as a martial artist to understand or 'see', and eventually, techniques will appear which no one taught you, you simply began to see them as being there. The techniques were always there; you are what changed. But you will miss all that if you learn kata A, then move on to kata B and never come back to practice A again.