Romeo that he wouldn't do the ceremony in hiding, like he wanted, Romeo would have been forced to either tell his parents, or have the ceremony openly and suffer the consequences.
Many would blame the terrible circumstances on fate; but, Friar Lawrence not only makes one but three mistakes that could have altered the play completely.
Firstly, right after Romeo is banished Juliet comes to him for help; however, instead of being an adult, he gives her a poison to put her in a deathly sleep. Friar Lawrence is a major character that has a lot of pull in the play, but he’s also easily pushed into things he shouldn't agree with. When Juliet comes to him in hope of something to take her to Romeo he gives her a potion made of a plant. He gives an unstable 14 year old girl poison; there had to have been a better idea than that rattling somewhere in his brain. He comes up with this elaborate plan to trick the Capulets into believing their precious daughter is dead. They don’t bury her but put her in a tomb with others of both houses. She’s not even put in a casket. This then brings us to the second issue that Friar Lawrence make, he trusts people with things they should not be trusted
with. Friar has to find a way to tell Romeo about the plan to have Juliet put in a sleep then woke 48 hours later so they can run away together. He sends Friar John, his helper, to take the letter to Romeo, but unfortunately gets side tracked by a father and his sick son. When he finally shows up to his destination Romeo has already been told of Juliet's “death” and had left his house. Friar lawrence, if he had taken the letter himself, would have changed the ending dramatically. “Unhappy fortune! By my brotherhood, the letter was not nice, but full of charge, of dear import; and the neglecting it may do much danger.” He tells John that by him neglecting the letter much misfortune is about to happen. He knew the importance of the letter and wouldn't have been stopped hence saving both the lives of the young. The tragedy would have ended in another prince saves princess riding off into the sunset, two lovers in the night, happily ever after, but Shakespeare doesn’t do love stories.