When you buy a stock on the Wall Street exchanges you are buying the stocks from a short sellers who does not own the stock, or you are buying the stock from another person who bought the stock from a short sellers who doesn't own one.
The Wall Street firms essentially issue and sell the phoney stocks and deposit collateral with the bank which is frozen in the bank along with the sell prices of the "shorted" stocks.
The short sellers game is to sell the phoney stocks at a high price and then buy them back cheaper. They can't make a profit UNTIL they buy back the phoney stocks they sold cheaper.
If you pay a high price for a stocks and then sell it cheaper some short sellers is buying it back and making a paper profit in his margin account. You by buying the stock at a high price and selling it lower are just giving your money away to the short sellers.
Should you buy and hold at any price? Hold until the market price goes higher than your buy price. Maybe a long long wait. Or should you sell lower and give your money away to the short sellers and then try to buy in at a lower price.
Sometimes, the short sellers will try to work down the stock prices. They sell higher and buy back lower, sell higher and buy back lower...until the market keeps sinking. The short sellers don't have to buy back from a long owner, a person who paid money to buy and own the phoney stock, the short sellers can ALSO buy back the stock from other short sellers who short it at a lower price.
Anyway, the money the short sellers get into their accounts is frozen until they buy back the shorted stocks they sold, and if there is not enough money in the bank to buy back the phoney stocks the short sellers sold, the bank can sue the short sellers for additional money.
Buy and hold is not a bad stragegy, but a slow one. If you pay $40 for a stock, keep it, even if the stock is selling for 7 cents. You can alway buy more stocks if the stock price goes down. Your claim is against the margin bank account of the Wall Street short sellers, not against the name on the phoney stock. If the stock says "GM" your claim is still against the margin bank accounts of the short sellers who sold the phoney stocks, NOT against the assets of the car manufacturer which did NOT sell you the "GM" stocks or get the money from selling you the "GM" stocks.
The worst that can happen is a stalemate. The short sellers will REFUSE to buy back the phoney stocks they sold at a high price. The buyers of the phoney stocks will REFUSE to sell them at a low price and trading will STOP. The money will be frozen in the bank. The short sellers won't be able to get their money out, their collateral for the stock loans, and the buyers of the phoney stocks will not be able to sell the phoney stocks they bought and get their money either.
Sometimes, Wall Street is a mutual suicide pact. The people who sold the phoney stocks without own them lose all of their investment AND the people who bought the phoney stocks with their savings (or borrowed money) ALSO lose their investment.
They both agree to BURN the money. The bank keeps it.