Large changes in lift (flaps) must be coordinated with changes in thrust (engines) to keep the aircraft level or slightly descending. A large reduction in lift

Large changes in lift (flaps) must be coordinated with changes in thrust (engines) to keep the aircraft level or slightly descending. A large reduction in lift (raising flaps) will cause a aircraft to dive. A large increase in lift (lowering flaps) will cause a aircraft to stall -- and fall. Either of these changes would be recoverable if there were more thrust or more altitude, both of which are intentionally minimized during a landing.