William also admitted he had been left "very sad" while working as an air ambulance pilot because of the horrors he saw.
Speaking during a training workshop aimed at encouraging first responders to open up about their feelings, he said: "I couldn't put my finger on it, but you just felt very sad.
"And then you start to see the world very differently ... you start just getting very sad that the world is so hurt.
"It's only then you go 'hang on, you've got to look at this' because it's only natural that you sponge it and bring it in.
"For me it was the sadness, I really felt the sadness, I'd absorb the jobs I'd gone to.
"Sadly with the Air Ambulance you get a lot of deaths and I didn't realise the impact - I would go to the next one and the next one.
"We've got to somehow change that culture where we feel it's okay to say 'listen, this was horrendous, I really didn't enjoy seeing that, it was really brutal'.
"How do we talk about it?"
The prince admitted huge developments have been made in recent years, recalling how few high-profile figures were willing to speak out in the early days of his campaigning.
He said: "This was six or seven years ago and not one celebrity wanted to talk about it in public ... and now look at it."
In a speech to those gathered for the visit, William hailed an "extraordinary year" for the emergency services and warned there would be "scary" times ahead.
He said: "The months ahead will no doubt be uncertain and at points scary.
"But, thanks to the dedication and sacrifice of those of you working across the emergency services and in the NHS, I count myself and others in this country very fortunate."
