You don't need a lawyer on retainer, but it's probably good to know the phone number of one. If they can't take your case they will let you know and likely refer you to a colleague.
I've never had to have any sort of interaction with the justice system and have never talked to a lawyer (even a friend or in a social setting). I thought I was a proper adult for having a regular accountant I talk to once a year.
I keep the business cards of a couple of lawyers in my wallet. One I've dealt with on business matters (but certainly isn't on retainer) and one I know socially who does criminal defense. As you say, I figure if they can't help me personally, they'll know someone who can.
How do I know the phone number to a good lawyer?