We just found another person who accidentally traveled to Pompeii and immediately died in lava. That sounds painful! (Editor's note: probably too quick to be painful.)
We just found another thousand people who died of starvation in the wilderness!
We just found another thousand dead bodies in the desert!
We just found another person who was burned as a witch in Salem!
We just found another person who was eaten by the Donner party!
We just found another person who was eaten in Jamestown!
We just found another ten people who were eaten by cannibals in Africa or Asia or the Pacific islands!
Ooh, we found someone eaten by cannibals in Europe!
Oops, someone got sacrificed to the gods by the Aztecs!
A few thousand travelers just got killed by popping into war zones!
I wonder when we'll find someone with a successful traveling experience?
Make a movie
I'm thinking something along these lines (possibly inspired by Roots). "I am a time traveler." Sound of a whip hitting flesh. "I am a time traveler!" Sound of a whip hitting flesh. Sobbing, "I am a slave."
Time travel survivor
Take people and leave them in random locations. Film them and see how long it takes for them to quit. Rules say that if the person calls a friend, that's the same as quitting. This will help people realize how difficult it is to survive a time travel jump.
Given a random place and time, you are far more likely to die than achieve success. You have perhaps a four in five chance of drowning or dying of dehydration immediately, and a one in ten chance of starving in the wilderness. The remaining one time in ten, you only have to worry about suddenly appearing in some country where you don't speak the language. Possibly because no one spoke modern English (or whatever) more than a thousand years ago.
Most of the last 10,000 years weren't that great, and the typical modern person doesn't have skills that would transfer. Perhaps the most useful talent would be killing people, but a single skilled killer who doesn't speak the local language is likely to be killed by some group.
It is possible to succeed, but most people won't. It's hard to prepare for the general problem, as the randomness leaves too many alternatives. It's easy to encounter a circumstance that turns a survivable location deadly. Most people will need help from other people to survive, but not knowing the language and not having anything to trade mean that it's hard to get help.