You can probably tick off reasons why not to buy Veeva Systems (NYSE: VEEV) stock without trying very hard. Some might say that the stock is bound to run out of steam after racking up gains of more than 50% so far in 2017. More could predict that gaining new customers in the life sciences industry will be more challenging in the days ahead than they’ve been in the past. Others could argue that Veeva’s valuation is too pricey.