Most bowlers neglect the mental game of bowling. Which is why most bowlers scores are average even after many years of bowling. Mental game training is critical to a bowlers success. Any bowler who spends his money, time and countless hours on physical practice will certainly find that as soon as he or she starts practicing the mental game of bowling right at bedtime or naptime or just before bowling (both in practice and in competition) their bowling will improve by leaps and bounds. I have written more in depth on the importance of training the mental game of bowling on other pages in this site.
Bowling is 90% mental. Why? Because your mind controls your body. Your mind decides how your body, arm wrist etc is going to direct your ball over its mark and ultimately into the pins.