Try living in Japan, where you're generally forced to use the name in your passport, including any middle names included (with space) in given name.

Meanwhile a typical Japanese name is no more than three characters each for family and given names, but someone with a western name will have several times that, complete with spaces. And of course most of the companies running various websites and computer systems don't care, because foreigners are a single digit percentage of the market. If you're lucky you can use a separate but equal foreigner flow with fewer features available. (I am looking at you, JAL Mileage Bank and your SEVEN character family+given name limit!)

It is typically possible to circumvent this using paper systems, but that's a particular shame -- one of the nice points about online computerized forms is that it is easy to send them back and forth through browser integrated machine translation which can make them vastly easier to fill out.