.first() vs. .one() in craft 3
.all() returns a collection of elements, which you can loop through with a for loop.

.one() returns a single element, so you cannot use a for loop to access it. 

In this case you should just store the entry like:

{% set entry = craft.entries.section('thing').one() %} and then access {{ entry.title }} afterwards.

(Also keep in mind that entry is automatically populated for section URLs, so you may want to use another variable name)