Thnaks both of you, and thanks winstreak for taking the time for the clear video !
I understand what's going on here. By the way, exemple here was not very well chosen because my real problem doesn't involve the possibility to use the Else statement.
I can't post the all code but here is the segment that poses problems :
In here, everything works well when the highlighted line is not present (wait 1 sec) : Layer 2 is shown on screen (Red button and Fight text are on this layer) and when button is clicked, layer 2 is set to invisible and State is changed to its correct value.
But when action "System > wait 1 sec" is added, everything works the same but "system > set layer 2 invisible" is not triggered.
What happens here ??? I really don't get it.