If I ask you to pay attention to any tension in your shoulders, something interesting usually happens. They will spontaneously drop, with little intent on your part. What happened? You paid attention and the holding broke into awareness. You realised you were actively maintaining it. The truth became apparent. Becoming aware of a contraction is all that is needed to release it. Adi-Da often talked about the self-contraction in this way.
When you sit down to practice Vipassana meditation, you observe your moment to moment experience with the intention of seeing the three characteristics: anicca (impermanence, change), dukkha (unsatisfactoriness, suffering) and anatta (not-self). More accurately, you are tuning into the 3Cs, as they are always already the case. This is not a philosophical exercise – the practice is to stay at the immediate sensate level of your experience, with a degree of mental calm that allows you to observe manifesting reality without getting caught up in it.