In chess, the 50-move rule, introduced in the 1500s, is designed to prevent a player from senselessly prolonging a game where he has a small advantage but no real hope of winning. It says that if 50 moves pass without a capture or pawn move, either player may insist on a draw. For some time it was thought that all winnable positions could be won or simplified within 50 moves, so that the 50-move rule would not change the value of any position given proper play. Then in the 20th century some positions were discovered that can be eventually won, but not in 50 moves. The rule was briefly modified to allow more moves when such a position arose, but eventually this was considered too complicated and the traditional rule returned in 1992 (thanks to Wikipedia for the history.)
I propose a modification to the rule: If Bob wants a draw under the 50-move rule but Ann thinks she can win, she may insist on an extension of 50 moves. There is a cost, however: If Ann fails to win the game, she scores a loss rather than a draw.
The idea is to avoid an outcome I think most chess players would find contrary to the spirit of the game: Ann knows she can win in a few more moves, but the rule kicks in and it’s a draw. When the extension is invoked (which would surely be quite rare), we know it’s not a waste of time — someone will win the game. I don’t know what the wisest length is for the extension, but 50 seems reasonable. It’s doubtful any human being would have the confidence to gamble on the extension if victory isn’t coming within 50 moves, anyway. Of course, you could let the extension length depend on the position, but this would again result in an unwieldy rulebook, which was the objection to the variable-move rule which was briefly in effect.
By the way, the world record, established by computer search in 2008, for moves necessary to win a position with optimal play is an amazing 517!