NES is a "When...You can..." effect, meaning that is must be the last thing to happen in order to activate.
Did you chained Navigation to another card? You can't start a new effect in the middle of a chain resolving, you have to wait for the chain to finish first, which means the last thing to happen would be that another card resolving, not Navigation resolving and NES being summoned.
Notably, there's a third kind called Mandatory "When".
It's an effect where the text just says "When" without "You can", meaning there's no choice, you have to do what the effect says (hence mandatory). This kind of effect cannot miss the timing as well.
Anon
Anoymous
