Many companies (and government agencies) assign customers ID numbers.
This is completely reasonable. At certain scale, when correctly ascertaining identity is vital, a unique identifier is a basic requirement.
But most companies don’t even try to make the user experience around ID numbers easy.
Take JetBlue, for example. Here’s the user drop-down menu on JetBlue’s website:
The TrueBlue number is a 10-digit number. There are no spaces, dashes, or other visual separators to make it easy to read. To make matters worse, as of the time of writing, trying to copy the number requires you to open developer tools (in Chrome and Safari, at least) ; for some reason the element isn’t even copyable for most users.
If you call JetBlue customer support, which the website instructs you to do for virtually any checkout error, the TrueBlue number is the first thing they ask you for.
ID Numbers are a perfect example of those tiny little design elements that can make or break a user’s experience. These little things add up.