In school, students are often taught about iambic pentameter via Shakespearian examples. These, however, were based on the Received Pronunciation (RP) reading of Shakespeare's works. In reality, Shakespeare used an entirely different pronunciation, replete with differences which removed syllables relative to Received Pronunciation.
Take the first stanza of Romeo and Juliet:
Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life;
Compare with the OP of the stanza:
How can iambic pentameter possibly work when the syllables that are meant to be stressed aren't even present?