Do you mean we should force user to accept the function as soon as possible?
No, make sure user know the business logic + calculate formula then accept, because some business logic only they know, they will help you too much, and they will know why need more man day
In Most Cases, Users do not know what they want to do so. It is the worst case. You may say User must know it and thus the project can be completed.
However, in real case, the situation is far from ideal.
Yes, you can ask user some real situation
Then new system, will bla bla bla, because bla bla bla
Don't let user think they should use which function before know business & system operate, they will create some useless / conflict logic waste our time.
Not everybody has systematic and logical mind set
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