Question I ask myself...because I have done it.....

Why do so many investors panic sell as the market declines? Are large numbers of investors just so lacking in self-control that they can't restrain themselves even though they know that they are acting illogically and against their own interests...

Some possible answers:
"One of the worst things that can happen to you in life is to win a bet on a horse at an early age."
-- Danny McGoorty (billiards hustler and author).

The worst thing that can happen to a young person who tries gambling is to win, because then the winner doesn't understand that it's gambling. People like to think they are in control far more than they are. Gee, these simple rules made money for me in the bull market, and if I keep doing them I'll keep having my own personal bull market, right"...
Agreed sometime the fast easy early win makes you less able to handle loss...markets are bit of a gamble I agree..

ALSO:
Because they don't understand what they own.

Some think investors who invest themselves are guilty of not doing their homework. According to a study...65% of the surveyed retail investors confessed that they had not even read their companies' 28% said they "skimmed them", and only 7% said they "studied them". ...- it's clear that the majority of retail investors don't do an adequate due diligence.
The main consequence of not doing due diligence properly is the lack of understanding of what they own and what if anything they believe the value is of what they have invested in...When the market falls, the lack of understanding leads to the dumping of their positions...

Lastly:
I made a previous posting on the virtue of Patience.
LACK of patience will lead many people to do the irrational thing out of fear,anger, spite,longing...whatever...
If we truly believe in the technology and the real store of value will we wait?

HOPE SO