[9YearLurker]

As I understand it, the stick shaker is supposed to go into effect to keep a plane from going into something like an aerodynamic stall — and a mechanical problem can lead to its activation.

http://www.airliners.net/forum/viewtopic.php?t=738385

http://www.abc.net.au/news/2017-04-13/qantas-stick-shaker-incident-explained/8442160

[xone]

As I understand it, the stick shaker is supposed to go into effect to keep a plane from going into something like an aerodynamic stall

It is to get the pilot to react to an impending stall.

and a mechanical problem can lead to its activation.

As could icing. The quality of the weather info provided to the pilots was noted during the mishap board. The board also cited improper reaction to the stall warning. Depending where the AC was inflight, it is possible it wasn't recoverable.