in my case, this year, the first frame is usually an over adjustment of speed or angle.  I have been bit too many times after a good 10th frame with a big split because the line had broken down.  many times it is a 4 pin or a split, so I usually change my line by a board or pick up my speed a little and leave a ten pin.  Also there is the case where I lose focus after a good finish and just don't release the ball correctly.  Name a mistake and I have made it.  This year, 795 and a 290 along with a front 10 289.  Along with an open 11 bagger 278.  Not so many 279's this year.  When I leave a pin, I usually end up leaving 1 or two more during the game.  Frustrated that the lanes are easier and I cannot seem to break the big one (300/800).  BTW Last year 214, this year 226.  At 61 years old, I don't think I improved that much.

300s aren't easy.  Ever.  They may be easier than they could be or should be, but not easy at all.  Hitting the pocket 12 times may be easy in some houses, but getting all 12 to carry is not easy.