As someone who has studied Chinese for a number of years now and who has lived in China briefly, I am still confused as to when to use 必须. For me, 需要 sounds more natural. Are they just used interchangeably? Or is one more written lang vs more spoken? Obviously there also 得, which is frequently used in everyday conversation.
Check out this lesson The Important Difference Between 需 (xū) and 须 (xū)! I think it might clear things up for you let me know if you want anything expanded on!
Thanks! That video really cleared things up for me!
It’s reassuring to hear that even native speakers have trouble with this one. Later on I looked up 须 and found out it depicts a bearded man. So I’ll remember it as being obligated to respect your elders.