Ask your players how their characters know, and tell your players what their characters know.
In the case of the truck crash, this is what those ideas would look like. As your players decide they're leaving the MacGuffin in a partly disassembled WeMoveIt truck, you say:
Okay, so how are you planning to keep an eye on this until you can come back for it? Tracking device, surveillance hack, dress up like a janitor? Drink at the Teamster bar and listen to them gossip?
It doesn't really matter what your players say as long as it's remotely possible. Now you have a way to get them on the exciting chase you want them to get on, so you present that information in keeping with how they get it. So if somebody volunteered to nurse a Shirley Temple all night at the Teamster bar, you can say:
Along about 1 AM, a group of people in WeMoveIt coveralls storm in, mood like an angry sky. Apparently the boss decided that an order really needed to get out tonight, in the fog, over the mountain road, in an old beater of a delivery truck they just patched back into service. When the union balked, he schemed up a way to saddle Babyface Jensen with it, and he's never even driven that route. Poor kid's gonna die out there.
All of that is just stuff any GM might say, but then you can follow up with what their characters know, things you don't intend to be a mystery to the players.
There was only one beat-up old delivery truck in that warehouse, and you hid the MacGuffin in it. And yeah, the kid's probably going to die out there, especially if he does the rookie thing and takes the bridge over West River to get to the mountain road. It's still under construction after that disastrous explosion last week.
So, what are you doing?
Of course, not everything you have planned can get the how/what going this easily, like the disastrous archaeological dig on a remote continent. What do you do in that case?
The players can't lose if they're not there.
Now, things can happen all the time when the players aren't there. Like, Babyface Jensen got pressured into that ill-fated drive. But the players haven't lost because Jensen's out driving, that's just something they have to deal with.
The thing is, unless you intend for something to be a campaign finale, having an action sequence that results in a campaign loss if the players don't succeed isn't that much different from having a fight which only ends when one side is dead. There's no guarantee the players will succeed at the action sequence or the fight, the dice could turn against them. If you don't want the players to lose or die you have to go in thinking: it isn't campaign over, so what's the worst that could happen?
So, if the players seriously screw up tailing Jensen and stopping the crash, or if even knowing the kid's going to die out there, are just too drained to throw their all into pursuing him, what's the worst that could happen? Well, the MacGuffin's now at the bottom of the West River. Probably a lot harder for the characters to secure now, and a lot easier for other forces to snag without leaving the obvious trail they would ripping it out of a truck in a busy warehouse. But not gone forever.
The same is also true of things you want to have happen without the characters necessarily having a way to find out, such as Dr. Bonn's ill-fated expedition to the tomb of Amok-Ra. If your game is geared more toward globetrotting adventure, like Spirit of the Century, players often have a hook to find that sort of thing out, like being a member of the Century Club, an international organization fighting to forward the better angels of humankind. The Century Club has all sorts of ready intelligence on threats all over the globe.
But if you're running in a setting where all the characters really have is their local newspaper, even if Dr. Bonn's expedition is front page news and the talk of the town, that might motivate the characters to get curious and get involved, but there's no indication how badly it's going to turn out if they don't. What do you do then?
Well, the players can't lose if they're not there, so you come up with a scenario that would get them more immediately involved. Maybe someone they care about really wants to go on this expedition and asks Dr. Bonn to hire them on, too. Or absent any ties like that, maybe they don't really lose to the evil of Amok-Ra until they get a chance to stop it on their own turf. Something like:
To complete his plan, Amok-Ra needs powerful artifacts that have already been entrusted to the state university, and since Dr. Bonn is one of their head researchers, he gets possessed. The expedition returns but with things more obviously wrong - Dr. Bonn the only survivor, bearing the Mark of Amok-Ra as a scar, with a bunch of mysterious packages in tow, and maybe the presser on his return goes south when he leaps into the crowd and nearly assaults one of the reporters before regaining his composure. Then you tell your players what their characters know - this isn't the same Dr. Bonn that left. This is some bad trouble. And they can start taking steps to stop it.
A final note: Not gaming is better than bad gaming.
If some or all of your players have had a bad week, to the point that they can't focus on getting into character or understanding the game world, there's no shame in canceling and just watching a movie or something. It's nobody's fault that the world is cruel. RPGs are a form of entertainment that need a decent amount of engagement on everybody's part in order to be successful. Trying to force that on people who aren't up to it at the moment is just going to give everybody in the game a worse time.