Convictions are beliefs - strong convictions are strong beliefs that the person feels are right. A person with strong convictions will not be convinced that these beliefs are false without a LOT of proof.

A fast person because it can get away from the strong person

To strong.

Neither is a strong and stable person.

It's not. Intelligence is innate and cannot be changed, but strength can be gained. S smart person can become a smart strong person but a strong person cannot become a smart annd strong person.