When are dictionaries more useful than lists?

Question :

When are dictionaries more useful than lists?

Dictionaries can be much more useful than lists when we wanted to store all our friends cell-phone numbers. We could create a list of pairs,(name of friend, phone number), but once this list becomes long enough searching this list for a specific phone number will get-time consuming. Better would be if we could index the list by our friend‘s name. This is precisely what a dictionary does.