Parallelism gone wrong...

Good parallelism means that in a series, each item begins with the same part of speech (verb with verbs, noun with nouns, preposition with prepositions, and so on):

Jackie runs to the store, buys food, and hurries home. (verbs: runs, buys, hurries)
Poetry takes years to learn, decades to practice, and a lifetime to master. (nouns: years, decades, lifetime)
To save him, the girls lifted the car off the curb, over his body, and onto the street. (prepositions: off, over, and onto)

Parallelism goes wrong when an item doesn't match its companions. What would happen if a door that hangs on three hinges had one hinge on backwards? The door wouldn't open. Similarly, faulty parallelism makes the sentence difficult to read:

X    Jackie runs to the store, buying food, and hurrying home.