Or you could say strong and comfortable - this is how you should feel doing yoga. There are different translations of the Sanskrit terms sthira (steady, stable, strong) and sukha (comfortable, light, ease). Whichever phrase you prefer, the practice of yoga should contain these two principles so that in any movement or pose, you should feel steady - & better to take a gentler/softer version of a pose that feels steady (say, the basic version of Tree, with one heel against the other ankle) than struggle to achieve a more advanced version (say, foot against the groin in Tree), whilst wobbling and straining in a very unsteady fashion and/or holding the wall. Its much better to perfect the basic version, where you can feel steady & therefore comfortable & then move on from there to the more advanced. Staying steady and comfortable will help you avoid injuries.
The lightness and comfort of a pose also comes from practice, as your muscles learn to work together effectively for maximum result with minimum effort. Compare the first time you tried downward dog, when the (dead!) weight was all falling through your shoulders to now - even just 4 classes later - when you can push the weight backwards towards the hips and enjoy the stretch through your back, feeing steady and comfortable.
These two principles emphasise the uniqueness of yoga as the best holistic practice for body and mind!
