BPL's purpose is to provide an entertaining league that will increase the fan base and make professional cricket an lucrative career choice for the talented ones (and some not so talented).
The immediate success of BPL is going to be based on fan excitement over cricket and improvement in domestic player performance at the T20 level.
Success in terms on national team will still be the responsibiilty of the board, the coaches and the players. It would be wrong to either fully credit or blame BPL for that.
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