I'm sorry to ask an unclear question, I don't sleep properly and when I do so, my English doesn't get any better, does it?
I created a pen actually, here: https://codepen.io/coolesterman/pen/gmJxpY?editors=0010
Explanation: Effect in and effect out only affect the blue square.
every time you click on "create/update animation" button, every tween related to the blue square will be removed from the time line and the state of the blue square will reset, and then it gets two brand new tween for coming in and getting out.
Problem: OK what is the problem now? if you select the "left" for the effect_in and hit "create/update animation" you will see the Blue Square immediately jump to the left, so we can see the tween affect it, but then if you select "fade" from the effect_in and hit "create/update animation" to create new animation, you'll see that the Blue Square doesn't get the opacity of zero at the start point. When I hit the "play" button it will work as expected. But why can I see it at the first place?
Best regards