Everyone has far more lapsed relationships than maintained ones. Fading is natural, and any of them can be pulled back off the shelf.
The idea
Nassim Nicholas Taleb popularized the antilibrary: the books you own but haven't read yet. I have about 200 on mine. My antilibrary of relationships I haven't maintained, despite wanting to, dwarfs it. That's normal. Robin Dunbar's research shows we keep people in concentric circles, and the closer the circle, the fewer people fit. Over time people drift outward: active clients become past clients, then names on a mailing list. Friends fade into acquaintances. Those downgrades make room for new closeness. And like a book on the shelf, a faded relationship is still there to pick up.
How to do it
Drop the shame. Losing touch is how our wiring works.
Think of someone you'd love to reconnect with: a past client, or a good person you'd rather have back in your life.
Pull one off. Notice the voice that says "if I really cared I'd have kept in touch." That's your ego protecting you from rejection, and it's usually wrong.
Send a short note (see Reconnecting After a Long Silence) and leave the ball in their court.
Example
Remember the last day of summer camp, when you hugged, cried and swore you'd be friends forever? Most of those faded, and that's fine. The other person almost certainly knows you drifted too, and may be feeling the same shame. Assuming you didn't set the bridge on fire, they'll probably be glad to hear from you.
Watch out for
Writing off lapsed contacts. Past contacts are a great source of business, and referrals are one of the best ways to grow any business.
It's Never Been Too Long: Relationships have no expiration date. After any gap, assume they'll be happy to hear from you, and reach out with no agenda.
Reconnecting After a Long Silence: Skip the apology. Send a short note that they came to mind, ideally with one real detail or shared memory, and leave the ball in their court.
Seasons of Your Network: Diagnose your season (planting, nurturing, harvesting or hibernating), match your effort to it, and give yourself permission to say no when it's winter.
The Down Escalator: Every relationship rides a down escalator, so ending one just means stepping off; stop investing, decline politely, never ghost, and leave the door open.