shoppers with just a few flavors of jam to choose from are more likely to buy than those given dozens of options (including the original choices). It’s as if we’re paralyzed when we have a large number of options to choose from, and so we end up getting nothing.
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Significantly more students bought the pens when there was a middle number of choices than when there were either high or low numbers of choices. So we appear to prefer a moderate number of choices — not too many, and not too few.

Shah and Wolford believe that purchasing patterns are likely to be similar for a wide range of products — although depending on the particular product, the optimal number of choices might be higher or lower than the 8-12 range they found for roller-ball pens.