If you have an event that's like "var1 > var2", this event will keep happen every tick when var1 > var2.
The green arrow means that the event is a trigger, so it indeed does trigger only once, but you if you have one in a sub-event like this:
var1 is less than var2
|- trigger event
Since var1 is less than var2, the trigger will keep occurring every tick also.
If you want to check if var2 is less than var1 and then only trigger it once, you have to use the system event "trigger once while true". So it would look like this:
var1 is less than var2
trigger only once - do action