Because sometimes we get through to them. It can make them more cautious or make them analyze the situation when they would have just jumped in without thinking.

With Jace, he was so used to being alone, he never thought of having someone worry about him or that he should care about getting hurt.

[Letting out an audible sigh, Alec rubs his chest, remembering the agony that'd he'd felt when Valentine sacrificed Jace to summon the Angel. He doesn't talk about it often, usually only with his family, but Rey won't tell anyone that would endanger Jace.]

It did get Jace killed.