Why, according to Paul, must every man believe in Chance and trust his luck?

Paul believes that all soldiers believe in "Chance" in the trenches; he cites a lucky incident in which he barely escaped being killed twice in a row.Really ending up alive in the trenches is based on chance and luck more than anything else.

"It is just as much a matter of chance that I am still alive as that I might have been hit. In a bombproof dug-out I may be smashed to atoms and in the open may survive ten hours' bombardment unscathed. No soldier outlives a thousand chances. But every soldier believes in Chance and trusts his luck."