Apart from other factors which require much deeper sequencing than 1x (usually 20x is a bare minimum), one fundamental thing to keep in mind is that you have 2

Apart from other factors which require much deeper sequencing than 1x (usually 20x is a bare minimum), one fundamental thing to keep in mind is that you have 2 copies of most of your chromosomes. So 1 "read" of that position of your genome intrinsically cannot tell you about both of them. The 20x requirement is in part driven by the simple statistics of getting enough reads that you're very unlikely to miss both chromosomes (think tossing a coin 10 times - 1/1024 chance you get 10 heads, extrapolate across 10^9 bases, if you hardly ever want that to happen you'll end up going for something like 20x at every position).