要 first drew a body with hands framing the waist — it was the original character for 'waist' (now 腰). The waist is the body's pivot, so 要 slid to 'the crucial point', then to wanting and needing what's crucial.
要 is one of Mandarin's busiest words: 我要 I want, 要不要? want it or not?, 重要 important, 只要 as long as, 要是 if. Learn 要 and you can order food, make plans, and state conditions — the language's load-bearing beam.
Hands on the waist — the body's pivot — everything IMPORTANT, everything you WANT.
要 doubles as future tense: 我要走了 'I'm about to leave'. Wanting and being-about-to share one character — desire as forecast.