That 'old lady who swallowed a fly' is an important bit of wisdom.
How many times have you read people here who got loaches for snails, or Loracarids for algae, not because they wanted them but because they thought a problem would be solved by them? Then they discover the pleco gets too big, or the loaches are miserable alone, or the fish they bought to eat the overpopulation of guppy fry eats guppies, or, or, or....
Not to mention the big picture of introducing non native species for various ideas and having them run wild and need controls, that need controls, etc.
I hadn't been on forums long before that poem my grandmother used to think was so funny started popping into my head all the time.