Yeah there are plenty of programs where you can tell whether they terminate or not. The proof that the halting problem is decidable has a self referential compo

Yeah there are plenty of programs where you can tell whether they terminate or not. The proof that the halting problem is decidable has a self referential component and most programs aren't self referential like this, nor do they make any library calls to halting problem deciders :). I think it's OK to do this simlification in a simple post like this, but important to keep in mind that it's a simplification. To make it more concrete, if you take a bunch of heuristics like scanning for while(true) {}, scanning whether there are any loops at all, discarding primitive foreach loops that have a linear relationship to the input data amount, etc, you have built a rudimentary halting problem decider that has 3 outputs: "will halt", "won't halt", "I don't know". You can make it better with lots of research, SAT3 solvers, etc, but ultimately you will have to accept that there will always be programs that the decider will output "I don't know" for.