If you speed too much during the flight, the

The plane is..
1.
If you speed too much during the flight, the aircraft cannot withstand the air resistance and break the wings.
A large ship with tens of thousands of tons is sailing at full speed, and all of a sudden, if you anchor it... the equipment you were holding on to the anchor can't hold up and it pulls out and breaks the whole thing. That's what airplanes can do. Although m is much smaller and v is much larger than ships.

Even a fighter jet that can fly Mach 2 or higher in the stratosphere can fly only 6-700 kilometers per hour at a low altitude near the back of the neighborhood. The aircraft will also experience much worse fuel efficiency. The air resistance is much stronger at lower altitudes.
However, historically, there have been cases in which fighter jets flew in such a low-flying manner in order to keep them off the radar of the enemy during operations.

2.
On the other hand, if the plane goes too slow..? It doesn't have enough lift to fly the plane, so the altitude goes down and later it crashes.
Just as an automobile engine has the lowest rotational speed to maintain its engine, there is a minimum speed in an airplane so that it does not fall into stall. An object moving in the air attaches in proportion to the square of the speed of both air resistance and lift.

When an airplane slows down, it is difficult to control its posture. However, landing requires this maneuver. It is difficult to deal with when a problem arises around the runway during landing and needs to float again.
Airplanes with strong thrust, like fighter planes, can quickly float again without much difficulty in this case, while large and fat airliners can cause accidents because it is difficult to respond quickly.

Of course, fighter jets are more maneuverable than airliners, but they also conduct much harsher maneuvers that airliners do not expect. As a result, there is still a risk of accidents.

3.
If the plane is overloaded, it can't take off even after exceeding the runway, causing an accident on the runway.
Even if the weather is so hot that the air density decreases, that alone makes the runway longer and it becomes difficult to take off.
Even after flying in the sky, the weight cannot be distributed, so if the gas tilts to one side.. It can also fall into the stall and lead to a fall. Conceptually, it is similar to a ship being tilted to one side and turning over.

It is important to keep in mind that airplanes, unlike cars and ships, are very critical and important means of transportation with their posture, shape, and surface condition.
It is not simply to reduce weight to remove snow and ice from the surface on a snowy day. Even such snow affects the lift around the plane.

And if the plane overstretches its altitude above the cruising altitude..? Eventually, it runs out of air, can't burn fuel, and the engine stops running. Then it crashes..;; The plane shouldn't try to mimic the rocket.

4.
Cars talk about how many cylinders a car has in one engine, while planes just count the number of engines. These days, planes are just two pairs..
Cars seem thread-oriented and planes seem process-oriented. =_=

Cars implement this as a device called a transmission because they need different characteristics of force when they start at rest and when they run at full speed.
But when you get to the airplane level... start - subsonic - supersonic - hypersonic - hypersonic... you need a completely different engine for each speed zone.

At subsonic speed, supersonic engines are extremely inefficient and inefficient. In the past, Concorde was unable to operate as fluidly as KTX would between conventional lines and high-speed lines and faced a Gyereuk-like situation. This is due to the fact that an airplane is not a train.

Conversely, a hypersonic engine such as a ram jet cannot start at rest.
Therefore, transportation that can combine an airplane and a space launch vehicle with one engine and one body without separation is currently the realm of science fiction in human technology.

5.
It's only natural, but planes are designed to get the maximum lift at high speeds.
However, sports cars are designed to be equipped with a stick called "air spoiler" in the back so that there is no lift and the body does not float even during high-speed driving. It is the opposite of an airplane.