I find that no matter how a bowler bowls (meaning form, type of release, number of steps, ball used, follow-thru, line thrown, etc.) if they do it consistently, they become pretty good bowlers.

I have seen bowlers average 220 + on a THS doing many things which the "books" say is wrong. Poor form, lousy mechanics, bad balance at the line and many other incorrect things do not seem to hinder them from being the top bowler in many leagues.

What I do see is that they are performing the act of bowling very consistently, doing whatever they do exactly the same time after time.

Even with bad mechanics, they do it the same all the time.

Therefore, I have come to the conclusion that consistency is the most important aspect of bowling.
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What's with the Braille on a drive-up-ATM?
Never under any circumstances take a sleeping pill and a laxative on the same night.

My initial observations of what separated a pro bowler from a good house bowler was just that: consistency. And that feeling hasn't changed from watching many pro tournaments and many high average scratch leagues. The pros throw the ball the same way every time (unless they CHOOSE to throw it differently), which makes them much better at knowing when to make adjustments, as well as much better at reading the lane. They also tend to get great roll on the ball, although I noticed the differences with ball roll much more so in the urethane days.
There are guys in my scratch leagues who get all over the ball and throw it better than many pros that I've seen, but they're often all over the map with ball speed, release, hitting their marks, missing spares, etc.
Consistency is absolutely the key to achieving greatness in bowling, IMHO.
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You weren't unlucky when you left that corner pin, so shut up about it already!!

Consistency is the name of the game.  However, I think KNOWLEDGE is the key to everything.  Granted, everyone wants to be consistent.  But, at the end of the night, 690 is 690 whether you go 230-230-230, or 250-190-250.  What separates the pros from ourselves, is that they too can be inconsistent at times, but it is KNOWING what to do and when to do it if the lanes call for it. I believe that you have to have the knowledge before consistency can happen.
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If anyone out there is worried about the scores being too high, try duckpin!!