I often wish I could find a way around the problem. It's like having two-year-old twins: they would be so much easier to handle one at a time. Like twins, they are often hard to distinguish, especially when found together. Strength. Stretch.
If the goal were just to cultivate strength, we could learn enough and repeat enough so that the neural pathways would be deep and reliable and we could count on having what we needed. If the goal were just strength, we could dig deep and find what it takes to hold ourselves together and to have an impact.
If the goal were just to stretch, we could take just one step, pull just one more fraction of an inch, open our minds to just one new idea at a time. If the goal were just stretch, we could free our imaginations and reach out. We could enjoy being pulled out of shape and out of orbit.
Growth for people (and trees, for instance) demands that we develop both strength and stretch. They demand different qualities, different practices, different perspectives. Just when we think we are ready to enjoy one, we become aware that the other needs our attention. Stretch too far, and strength suffers. Get too used to being strong and you lose the urge to stretch.
It's hard to find comfortable models of excellence. Whether they are motivated by pain or by gain, models of excellence move endlessly between the need for more stretch and the need for more strength. They reach and contract and imagine and build. They are unsatisfied and generally unsafe. They are not content.
They are often joyful. They are fulfilling the most natural of imperatives. They are growing.