In previous versions of Minecraft (including 1.12), the following command worked:
/give @p diamond_helmet 1 0 {display:{Name:"John Smith"}}

Now with the new command parser in Minecraft 18w14a, the command will not work unless you escape the quotes as follows:
/give @p diamond_helmet{display:{Name:"\"John Smith\""}} 1

The new way requires additional characters making the command longer which is harder for people to type (and is easier to get wrong) and uses up the limited number of characters allowed before needing to use a command block. (This is also a problem for CustomName.)

Please fix the Name and CustomName tags so that they do not require the additional escaped quotes. For example:
/give @p diamond_helmet{display:{Name:"John Smith"}} 1