This particular phrasing comes from Norman Fischer's book Training in Compassion, but it is an idea we are all familiar with to some extent.
The basic concept is to deliberately re-interpret bad circumstances as opportunities for growth.
It's not about being passive and letting go of any preferences for how things should be. It's about not wasting our energy fighting against what is.
This orientation to life becomes self-fulfilling, because it helps us shift out of frustration and despair in the midst of whatever crisis we find ourselves in, which changes our experience of the situation and what is possible for us in it. It increases the likelihood that we will be able to access thoughts, feelings, and actions that are creative and skillful. It trains us to look for opportunities in the midst of hardship.
It is perhaps most obvious to heed this advice in the face of great hardship. When our world is turned upside-down by a mistake of ours or some unforeseen event. It's easier to see the futility of our internal resistance in the face of a major upheaval.
Far more common in the average life are the subtle, near-daily setbacks and frustrations that we encounter and resist internally. The difficult person who happened to get in line before us at the grocery store and is fuddling around with loose change. The slow-moving traveller taking too long to put their luggage in the overhead bin. The noisy or smelly person on the train next to us. The person who is not enough of something or too much of something else (often this person is us!). Not kind, smart, friendly, interesting enough. Too kind, smart, friendly, interesting.
These moments are often overlooked opportunities to apply and benefit from the cliched wisdom to turn lemons into lemonade. They provide a daily training ground to transform our lived experience and become more relaxed, confident, and kind people. We need not wait for a personal disaster to learn this lesson (although few of us make it to the end without our share of disaster!).
A teacher of mine, James Flaherty, offered this reflection: "What in my experience am I resisting? As being not enough, or too much?"
You could try asking yourself this question a few times each day.
I suspect if you put this into practice, you'll be surprised to see how often you resist reality. Learning to transform the subtle ways we resist what is unfolding around us frees up a tremendous amount of personal energy.