Multi-bagger or Falling knife.

 "The best thing that happens to us is when a great company gets into temporary trouble ....  We want to buy them when they are on the operating table."

Warren Buffett

(e.g. American Express)

"A stock that has fallen 90% is a stock that fell 80% first and then halved."

(e.g. Valiant bought and sold by Bill Ackman)

Reasons for steep falls

• Leveraged financials and loan/other losses.
• Food and other consumer products - safety, ingredients, etc.
• Victim of fraud
• Perpetrator of a fraud
• Unethical / Illegal behaviour
• Loss of key customer / product segment/ market
• Regulatory issues

Beware of COMMITMENT BIAS when you already own a stock.  

This is a difference between the buying of American Express by Warren Buffett (putting 40% of his fund in this company) and not selling and buying more of Valiant by Bill Ackman.   These are high risk, high return situations which can have extreme results (binary event).

Beware of LEVERAGED FINANCIALS

In banks, shareholders' money is 8% to 10% of its assets.  90% are borrowed money.   A slight mistake can wipe out shareholders' money.  Steep losses seen in bank, investors should avoid it like the plaque.

(e.g Deutch bank)

Food / Consumer brands - SPEED BUMPS?

Unintentional loss at the quality level that can be rectified.  (eg,  lead content in Maggi noodles of Nestle).   These companies are not leveraged and usually bounds back in one or two years after taking a hit.  These are buying opportunities.  Speed bumps and not end of the road catastrophe.

Gangrene amputation pattern

Maybe alright to participate in the surviving business after the "bad segment" is disposed.

Drug companies involved in law suits due to side effects, generally avoid.  Outcome is uncertain.  If it is just technical or production issues, maybe an opportunity to own, as these are usually temporary and solvable.

Unethical / Illegal Behaviour

Wells Fargo beefed up its top and bottom lines through hard selling a few years ago.  This unethical behaviour led to its stocks being hammered down.  Is this a great company?  Is the event a temporary threat to its business or a permanent life threatening catastrophe event to its existence?

B2B Quality / Other Issues

Foxconn workers committing suicide in China.  Is this a temporary issue or is it a life threatening existential threat?   This will guide you whether to buy or not.

Product quality issues.  How many customers have run away?  1 customer or many / all customers.

Solution is product recall and replace.  Example recall in cars due to certain defects.  Temporary issue.

Additional notes:

September 2016

Wells Fargo's fake accounts scandal surfaced in September 2016, revealing that employees at the San Francisco-based bank had opened millions of fraudulent accounts, often to meet sales goals.