Question: Why I can't feel the actual speed of plane when the plane in the sky? I mean I cannot judge how fast the plane is going in terms of the light on the ground and I feel it is flying so slow. How can I explain this mismatch?

Answer: 
You do not feel speed, you only feel acceleration, or other forces, like those from the wind on your face - and you cannot feel that in a plane.

So you do feel something when the plane is accelerating, taking off, sometimes when it banks, or in bad weather.

But a plane's speed is typically steady, unchanging, for most of the trip.

When changes in the plane's motion occur they are relatively small (except for very bad weather, jet stream turbulence and the like ). The plane's motion is normally kept within reasonable acceleration rates for the precise reason to avoid passenger discomfort (and to avoid excessive stress on the airframe).

So you're in a system that's designed to minimize your sensation of motion.

As you're high up, you cannot see how fast the plane's ground speed is. The closer you are to a passing object, the faster you think you're going. You're not close to the ground so it almost drifts by.

A similar effect is why some people experience more fear when driving that others. They concentrate on the road surface near their car and it gives a greater impression of speed than the place they should be looking (further ahead). You might also notice it if you were on a skateboard and compared the sensation of speed when standing to that when kneeling.

The speed doesn't change, but your brain picks up different clues to motion and interprets them as different speeds. In a high flying plane there are no obvious speed clues so your brain can interpret that as not moving fast.
I believe it's an illusion that has to do more with cognitive science. The treatment of objects movements and the evaluation of their speed is done pretty unconsciously through different visual areas of the cortex. [Some people for example cannot perceive](https://en.wikipedia.org/wiki/Akinetopsia) motion even though they see perfectly well! This information is also completed by other sources of information that help us "feel" the speed like feeling the wind, vibrations, noise and eye movements.   

So the feel of speed is not a rational process! Most likely it was developed to help us hunt or escape the attack of an animal. But not to judge the speed of an aircraft.   

Then somehow all this information reaches [Speed cells](http://www.sciencemag.org/news/2015/07/speed-cells-brain-track-how-fast-animals-run) that among Place cells, Grid cells, Boundary cell and Head direction cells form the "human GPS system". When in a plane, all the information reaching the speed cells is biased and thinking rationally about our real speed can't really change the slow "feel" of our speed cells. Maybe a lot of training could help. One should ask test or fighter pilots if they feel the real speed.

 People who vote your question down should get [a life.](https://www.cheaptickets.com/)