Now, in the spirit of ´debunking myths´ one might say this were not true, because they also protected the troops against (machine) gun fire. So: #11: ´Trenches were made to dug arti-fire - Actually, the first trenches were dug to hide from small calibre fire, like rifles and machine guns. Many more small calibre bullets missed they intented targets, because of trenches, than arti-shells´
Trenches were dug to protect men from the massive firepower of the WW1 battlefield. They significantly improved your chances of survival against all types of armaments available in 1914.
Somebody I read once (AJP Taylor?) made the point that atrillery was they only thing that could destroy trenches and one of the reasons for the initial digging of trenches was the volume of small arms fire was too large to allow operations in view of the enemy. The shortage of artillery and amunition on all sides after the first months of the war prevented them from blasting through the shallow, single line of trenches that had formed to that date and allow some form of mobile operations to occur. By the time armament manufacture had caught up to the needs of the beligerents (around 1916 for most nations) the trench lines had become deep and complex enough that simple weight of shells was no longer sufficient.
So the trench lines appeared partly due to modern artillery and partly due to a lack of it.