from the documentation:
However, triggers are an exception. See the green arrow to the left of Keyboard: On Space pressed from the previous example:
An event with a triggered condition
This indicates the event is triggered. Rather than running once per tick, this event simply runs (or "fires") upon something actually happening. In this case, the event runs when the user hits the Spacebar key on the keyboard. It is never checked any other time. Since triggers run upon an event happening, they aren't checked in top-to-bottom order like other events. This means the ordering of triggers relative to other events is not important (except relative to other triggers of the same type, since triggers still fire top-to-bottom).
There can only be one trigger in an event, because two triggers cannot fire simultaneously. However, multiple triggers can be placed in 'Or' blocks (see the next section).
https://www.construct.net/en/make-games/manuals/construct-3/project-primitives/events/how-events-work