Vitamin E is short in far more diets than most people would guess: US national survey data (NHANES) suggests around 84% of people don't get enough to meet the recommended intake, one of the higher shortfall figures among the vitamins.
Its main role is as an antioxidant, protecting your cells from damage, and it supports immune function. Clear symptoms from low intake are uncommon in otherwise healthy people, since the body holds a reserve, so this is less about noticeable effects and more about topping up a supply that quietly runs thin.
Adults need around 13 mg a day, from nuts and seeds (especially almonds and sunflower seeds), vegetable oils, spinach, and avocado. Because it's a fat-soluble vitamin the body stores, it carries an upper limit: it's best not to exceed 100 mg a day, a ceiling that essentially only comes into play with supplements.