If the difficulty of the challenge is very low, and the player’s skill level is high, the player will be facing boredom.
If the difficulty of the challenge is very high, and the player’s skill level is very low, the player will be facing anxiety.
None of these feelings are very good when playing and practicing golf. No one wants to fell bored when practicing, because then its not really fun right? Neither wants anyone to feel anxiety because the challenge is so difficult that they fell useless.
This means that the way you practice must be well balanced according to the difficulty of the challenge you are facing, in order to enter the flow state of mind. It may not be easy because then the player will be bored. Neither must it be way to difficult, because that can break the player completely.
A very good drill to try would be the zone-climb, which can be found in the free e-book Top 3 chipping drills. This drill is constructed in a way that it automatically makes it more and more difficult the better you perform, which makes sure that you can enter the flow state of mind easily.
One last comment about the difficulty of the challenges:
I better like to make games and drills a little to difficult than to boring. I am a strong believer the practice should frustrate you, and sometimes you should be on the edge of breaking completing. In these situations you learn so much more about yourself, and hey, isn’t it exactly those feelings you sometimes get when you play?