This rule is confusing for people who play primarily type 1 because the only real common situation where this comes type of rule would apply, has an errata to make it actually NOT follow the rule: the card is Goblin Welder.
Here is the errata:

: Choose target artifact a player controls and target artifact card in that player's graveyard. If both targets are still legal as this ability resolves, that player sacrifices the artifact in play, then puts the other artifact from his or her graveyard into play.
Making 1 target illegal in this case causes the entire effect to not resolves only because the errata explicitly says so.