When pressing space during an elytra flight, extra durability gets used from the elytra. This makes it so that if you want to have a 1-use elytra that works like a parachute, then if you accidentally press space during flight, then you will fall to your death.

Use this command to get a 1-use elytra
/give @p elytra 1 430 {display:{Name:"ParaGlider",Lore:["ParaGlide brand","one-use glider suit."]}}

Jump off of a high place in survival, activate the elytra, then press space again during flight. You will fall to your death.

EDIT: Upon further testing, I discovered that this is not why the elytra fails. It is because the elytra uses up one durability per second of flight, and me pressing space when its durability was used up was a mere coincidence.