He didn't need any preconceived ideas about his little brother or sister.
The only problem is that it all doesn't fit into your preconceived plans.
Prenuptial agreements are created for people who approach a marriage with the preconceived idea that it may not succeed.
All experiments are fruitful if you don't have any preconceived notions about the results.
We will not go into this with ironclad, preconceived notions.