And I'd not fault you for doing that. For me, though, if I can make a ruling that makes sense and is quick, I'm going to do it. In the example I stated I'd just have the dagger thrower go first. End of story unless a player had a good argument for why I should make an exception. There wouldn't be a default towards making a check or checks.Not automatically successful. There's still the initiative roll.
But seriously, if I have to chose between 1) a perception check, and then maybe an insight check, and then maybe an initiative roll or 2) abstracting all that into an initiative roll, I'm going for option #2 almost every time.
I’d do that in some circumstances also.And I'd not fault you for doing that. For me, though, if I can make a ruling that makes sense and is quick, I'm going to do it. In the example I stated I'd just have the dagger thrower go first. End of story unless a player had a good argument for why I should make an exception. There wouldn't be a default towards making a check or checks.
I have no problem with it going both ways. Neither do my players.Whichever you choose, it should be symmetric: if the PC gets the drop on the NPCs in the scenario described, then the next time an NPC pulls something similar they should get a free attack.
Which is why I'd just roll initiative.
There is a resolution system. That system says that for ability checks, and initiative is an ability check, the DM determines if success is automatic, failure is automatic, or the outcome is in doubt. Only if it is in doubt and with meaningful consequence for failure do you roll.
I seem to be greatly in the minority here (a familiar position!) but IMO if someone sets off the powderkeg without warning it is - or should be - that act of setting it off that starts proceedings. This means that either the setter-off should act first if most or all others are surprised*, or should get a whacking big bonus on initiative if they are not.
I've had this argument with my DM numerous times, when I've in theory been the setter-off but by the time my initiative comes around my intended action would be nearly pointless.
* - don't get me started on 5e's garbage surprise rules as those are a whole other issue.
Han shot first!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.