Both are correct. For example in 120V systems it is a common practice in industrial circles to buy lamps rated for 130V because they will last longer. When 120V is applied to a filament designed for 130V, the filament wil be cooler than its design temperature and so last longer. When a manufacturer makes a bulb that is designed to last 750 hours, they specify a voltage rating based on the resistive attributes of the tungsten filament and how long it will take for the material to vaporize based on that temperature. At a lower voltage and the same resistance, the filament operates cooler (albeit with slightly less light output) and therefore lasts longer.
The loose connections can create thermal stress as well. Tungsten also has a positive coeficient of temperature, meaning that as temperature goes up, the resistance goes up. When you first turn it on, it is cool so the resistance is lower and therefore current tends to be high for a few milliseconds. That heats it up quickly so it reaches operating stasis and glows accordingly. If a loose connection is "flickering" the tungsten on and off rapidly it actually cools ever so slightly in between and the resultant spikes in current raise the instantaneous temperature beyond the design limits. Over time those temperature spikes cause minutely more vaporization of the tungsten and shorten the overall life.
It is all based on the same basic principal of electrical components:
Heat x Time = Failure.
Probably more than you wanted to know but there you go.
"Venditori de oleum-vipera non vigere excordis populi"