Notice that the stiffest tree is most easily cracked, while the bamboo or willow survives by bending in the wind.....Bruce Lee
Bruce Lee definitely had a Zen approach towards life, and what I think he implied from the above quote was about the importance of being responsive versus reactive when dealing with the unpredictability of life. This has a great deal to do with what George Mumford describes as mental suppleness-believing in one's ability to get quiet and stay connected to that space between stimulus and response. This takes an amazing amount of practice, because it often goes against our hardwired fight or flight impulse, and hence involves a degree of de-conditioning.
On the tennis court, I've had my own battles with anger, frustration and fear (being the stiff tree), all leading to hostility towards myself, my opponent, and nasty cycles of shame and self-loathing. It's actually what brought me to counselling, and my own practice of mindfulness, self-compassion, and generally learning how to be like the willow, more psychologically flexible and emotionally forgiving.
On another personal note, I was lucky enough to grow up with a big willow tree in my backyard, and was always amazed by the way it could withstand even the most brutal storms without a single branch breaking.
Unfortunately that tree is now gone, but the lesson has not been lost.
Be Like A Tree