Why did van Gogh paint the 'Pair of Shoes'?

This is like asking, "Why do Christians believe in God?" Only not as serious. Van Gogh paints things because of experiences, observations, etc-- The same reason everyone else paints everything. You cannot pinpoint one reason why one artist makes every painting. There's a reasoning behind all of them. The only way you would be able to know the exact answer to this question is if you spoke to Van Gogh directly and asked him why he made each and every painting that he made. Simple as that. Sorry for the overly long answer, but it's very difficult to explain in few Words without sounding mean or harsh.