Barkoe
The ladder is a tidy picture. You start at the bottom, climb a rung every two or three years, and retire from somewhere near the top. Most career conversations still use it: what is your next promotion, and when?
Careers that people actually have look more like water. They rise for a while, then draw back for a course, a child, a move abroad or a stretch of freelance work, and rise again somewhere else. That is neither drifting nor failure. It is a shape, and a manager can plan around it once they stop expecting a ladder.
Offer more than one direction
Some of your people want the next title. Others want a bigger problem, or a smaller one, or a different problem entirely. Some want to work four days a week for a year. If promotion is the only thing on offer, you serve the first group well and lose the rest.
Make sideways moves normal. Let someone spend a quarter in another team, or take on a project outside their remit. Say aloud that stepping back from management to the work itself is a fine choice, and mean it.
Leave the door open
People who leave on good terms come back more often than managers expect, sometimes within a year. They return with more experience, a wider network and a clearer idea of what they want. Keep in touch with them. A short message every few months costs nothing, and the day someone replies is the day you have a hire you do not have to interview.
Ask about direction
Once a year, ask each person which way they want to go, and accept that "not up" is an answer. Write it down and check it next time. What people want changes with the tide, and the manager who notices first is the one who keeps them.