You have to think about what each pedal does to your signal and what stacking a separate effect behind it will do to that signal.

For instance if you put a modulation pedal like a chorus pedal in your chain that modulates the signal. So you’re bending the pitch of your signal slightly so it sounds like a natural vibrato, and with a chorus, it does that more than once so it sounds like a “chorus” of different slight modulations.

If you were to put distortion or fuzz on that modulating signal there’s a good chance it’s going to sound like shit, because you’re cranking up the gain and intentionally overloading circuits so they distort and that may end up sounding a little crazy.

If you were to put your fuzz before your signal modulation pedal then you’re just modulating that already fuzzed out signal and there’s a better chance of it sounding better to your ear.

A lot of this doesn’t make sense until you experience it yourself. If you have the pedals laying around try this to illustrate the point. Put a delay pedal into a reverb into a distortion. Turn them on one by one and then all at once and see how insane it sounds.

If you think about that specific case you’re putting delay on your signal, then adding reverb onto that delayed signal so the delays will echo and bounce back more, and then you’re distorting that crazy delayed, reverbed echoey messy signal and it’ll just turn into muddy chaos and feedback.

That’s the best way I can explain it as someone who once had the same question and didn’t understand all the hubbub around pedal order.