The question itself is the answer
PANIC.
Everyone knows cryptocurrency market is highly volatile and risky.
And most of the people do emotional trading.
They sell when it is crashing. And suffer from the loss. They panic and sell in the loss.
What is the point in selling at low?
One must wait for the market to turn green and bullish.
The way to stop the panic is to not engage in panic-inducing activities such as day trading.
It is like the old joke; a man goes to the doctor and says my arm hurts when I put it overhead.
The doctor says dont put your arm overhead

If you are in need of urgent money than selling is OKAY but for profit,
HODL is the best.
For being a newbie you should not in hurry to invest or trade crypto without a proper knowledge about it's volatility. you need to wait for the best time, no one is late in investing crypto as investing can do everyday with a proper knowledge and experience. If you have knowledge you are far to panic in every situation as you know the proper remedy.