How do I catch car problems that only show up sometimes?

You catch most problems now. The ones that beat you are the intermittent ones, the faults that hide when you look and appear when you are far from help. Those are genuinely hard, so do not take being stranded as proof you are careless. Intermittent problems leave a trail even when they hide. Learn the early whispers: a smell, a sound, a slight change in how it runs, a warning that flickers and clears. Write them down when they happen, even small ones, so a pattern can form. The clue you dismiss today is often the breakdown you could have prevented. Trust the small signs and act on them before they force your hand. When something feels a little off but checks out fine, note it and watch it rather than forgetting it. Over time you will build a feel for the faults that come and go. You cannot catch everything, but you can turn those roadside surprises into problems you saw coming.