Plan B seriously !!!???

Most of the time for a specific objective in our life we  definitely have a plan how to achieve it , let's name it as 'A' obviously its our first strategy to do it ,,,,,,
Suppose,  we fail in that attempt we will be  having a subsidiary plan 'B' because , we need to achieve it , isn't it ???
But !! you know what..... what if I say that we shouldn't have a plan 'B' or 2nd try.... because i think it'll distract us form giving our cent percent to plan A or our first attempt......???