We use the word “should” an awful lot.
The problem is each use is an implicit judgement, and sometimes even an implied commitment.
The judgement part is simple. If you say “should” you’re looking at the current situation, applying your values, and determining what you think should happen.
“You should call your sister”, for example, communicates your judgement of value to another person, whom you feel should call their sibling. This statement is regardless of their feelings on the matter.
It’s all about what YOU think, not them (or even the sister).
It’s your opinion of which actions are proper for someone else.
The problem is our life is full, absolutely chock-full, of “shoulds.” It’s overwhelming.
I should eat better. I should do that errand. I should exercise more. I should … You should … We should … They should …
People rarely appreciate our adding another unsolicited “should” to their load.
And there’s no opt-out. It’s a value statement, not a question.
Maybe ask, instead?
“Have you thought about calling your sister?” “Could you do that errand soon?” This type of approach can be open, collaborative, and allows for accepting or rejecting. (*Cough* even “Maybe ask, instead?” instead of “You should ask instead.” 
)
It also allows for a dialog that might result in realizing it’s not something that “should” be done at all, or perhaps “should” be done differently.
There are always scenarios where “should” is the right word, don’t get me wrong. We should all be more kind, for example.
Life “should” also be fair.
It’s not.
The world does not care about “should.”
– Ryan Holiday – Courage Is Calling