Would fear be considered a good motivator?

Fear is a great motivator. You drive the speed limit for fear of getting a speeding ticket. I think it is good in most situations but not all. Fear in a relationship would be harmful. Such as fear of your partner committing infidelity. It could cause one mate to be too clingy and make the relationship fail. But then fear that your partner would leave you if you were unfaithful might motivate you to stay faithful.