Sometimes an optional effect can only be activated "when" a condition happens. In this case, you are only allowed to activate the effect when the activation condition being met was the last thing to happen in the game. If something else happened after the activation condition was met, then you have missed the timing, and cannot activate the optional effect.

Now fore some examples
If Gusto Gulldo was destroyed by battle or by a card eff (Like dark hole) he can activate his eff in grave to SS Gusto level 2 or lower. If gusto gulldo is a cost to pay for a card like Icarus Attack It will miss timing Becouse there are stuff happening after he goes to grave so it will miss timing and will not activate his eff.If you use him for a tribute/synchro summon it Will miss timing.

that is not in every effect e.g sangan says "when" and in a tribute or synchro or fusion summon he can not mis timing at all while something like black rose comes and boom the field while you used sangan in your synchro you still get sangan some eff says you can add up to now that is a effect that you do miss timing with in some case. e.g

e hero shining destroyed by ryko then shining miss timing due to ryko had 2nd effect

and yea no 1 is allowed to edit the lesson after posting it (this dose not go for admins,mod)

ok i just said example. but OK One thing happened to me while i was dueling six sams to
I attacked Hand with zero and i had a shining in atk he activated mirror force and i activated zero eff.He tought he can nagate it with musakani but since shining eff activates too he coulnt have.He could have activated it if only Zero was going to grave