Tamas is the heaviest of the three. Krishna says: know it as born from ignorance. It deludes all living beings. And it binds the soul through three specific instruments: carelessness, laziness, and excessive sleep.
Everyone has experienced its pull. The alarm rings but the body refuses to move. An important task sits waiting but the mind keeps saying "tomorrow." A clear decision needs to be made but everything feels foggy. That heaviness, that inertia, that reluctance to engage with life — that is tamas at work.
Under tamas, a person loses the ability to tell right from wrong (ignorance), the motivation to do anything constructive (laziness), and basic alertness (carelessness). It is the opposite of everything sattva stands for.