He didn't need any preconceived ideas about his little brother or sister.
Prenuptial agreements are created for people who approach a marriage with the preconceived idea that it may not succeed.
The only problem is that it all doesn't fit into your preconceived plans.
All experiments are fruitful if you don't have any preconceived notions about the results.
The opportunity to set aside preconceived notions about race, religion or color, and really take the chance to get to know someone different from yourself.