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.
Try to avoid panicking because it won't help you make wise decisions in trading. Always trust in your instict and to be more sure of it, always choose to invest and hold the best tokens. Try reading the platform of the tokens that you are holding upon joining so that you'll have an idea about it.