People say stupid things because they don’t know what to say.
I am eternally grateful to my mother, who gave me an etiquette book when I was a teenager. This was great for me, because I was socially awkward, and would frequently say some of these stupid things, or nothing at all, not out of malice, but out of awkwardness.
One of the chapters in the book was about things to say on all occasions. It reduces it to a formula, of course, but my heart thinks what it needs to, and my mouth says what the book says.
For instance, when you speak to a person who has just lost a loved one, you tell them how sorry you are for their loss, then recall an important moment in that loved one’s life, and tell why it was important to you. Also, you can speak of the virtues of the deceased person: you can never go wrong with that.
Knowing this “formula” made me less afraid to say something to a bereaved person. Even if I could not say what was in my heart, I could say something that would help relieve a small part of their pain, and that was important to me.
“I am so sorry that you hurt your <fill in the appropriate organ or system>. I hope you will be up and about and healthy soon.” works really well, too.