Siddhant Modi known as Sid was a spoiled brat, very immature, boyish, irresponsible kiddo, dressed childish, was surrounded by soft toys and games as you can see in the picture:
This cute Kiddo named Sid joins Sanjeevani as an intern Dr.Siddhant Modi, but doesn't take his duty seriously. Doesn't even respect his seniors and calls Dr.Shashank " Chill, dude"
He doesn't believe in dressing professionally and walks into Sanjeevani with his Superman, Spiderman, Cartoon character T-shirts. He is more about when would his duty end and when he gets to go home and play his video game instead of learning anything new as an intern and wouldn't actually mind playing video games on his laptop while at work in Sanjeevani.

There is a twist in his life when he is to be expelled from Sanjeevani and Tamanna stands up for him and as a result they both get sent to Safala and start respecting each other. Later when he finds out that his colleague Tamanna's dad is a sweeper, he starts respecting her dad- the same dude whom he offered money to clean up the bhindi from the floor and is proud of Tamanna for fighting tough circumstances in life and entering the medical profession.
Finally Dr.Sid par acchi sangad ka accha asar ho gaya. He started thinking about others too after being in Tamanna's company. Not only that he began to dress up properly too, he finally gave up his kiddo clothes and started wearing UB shirts
Kiddo gave up his spiderman and superman clothes and is wearing a UB shirt

Ranbir Style also suits the boy slowly turning into a man

Baccha thoda bada ho gaya. Par itna bhi nahi, he was still a boy who had hard time understanding his and others emotions. He was just being a stubborn boy demanding things, following Tamanna all the way to the chawl alongwith two other buddies. Tamanna helps him out with his feelings and makes him realize that he was just being ziddi and not actually in love with Tamanna and there will be a time in his life when he will find his true love. This boy says bye to Tamanna and hi to Ridzy but bechara has to face a lot of slaps from Ridzy and go to jail a few times. He tries to take revenge and things turn out to be disastrous, but wait, this boy becomes responsible and takes the blame on himself of what he did. Not only that he assists Ridzy in finding Armaan in Panchgani inspite of Ridzy not liking him.
Now this boy really started to grow into a mature man. He made sure to protect Ridz all the time. He saved Ridzy from hypothermia but got blamed of raping her. Situation gets complicated and Sid brings up the idea of marrying Ridzy to Dr.Shashank as an outcome to save his reputation in the society. After dramatic suicide attempt by Ridzy, Sid still marries her to keep her father's reputation and instead of making a fiasco about Ridzy's suicide attempt, he saves Ridz life quietly and doesn't even let anyone know about it. The marriage wasn't going that well, but slowly Ridzy started falling for Sid and wanted to improve their marriage and give this relationship a chance. Then enters Armaan - the love life of Ridzy before marriage.
Spoiled brat turned to a hubby
Our spoiled brat silly boy has become so mature now that he has learnt to give sacrifices, care about Ridzy's feelings more than his and at the same time has learnt to respect people. He calls his seniors aap now.
At the same time, interesting thing to notice is that this spoiled boy was on Dr.Shashank's blacklist, but now is Dr.Shashank's damad and was successful in gaining Dr.Shashank's trust in such a short span of time. This spoiled brat din't know what it means to see a guy for marriage and he got married over night. Not only that he himself went to see a ladki with his mom bcoz his mom din't know he is already married. He also lets his wife cry on his shoulders and let her feelings out where before he din't even care about anyone else besides himself. Itna hi nahi, he was afraid of going to Safala when he was a boy bcoz there were no pizza places in Safala, he was fussy for having to use well water instead of being able to use a shower, but this same kid chooses to live in Tamanna's chawl and stand in nal ki line. And now, as a fully matured man, doesn't even have any demands, just wants to see people around him happy. It is amazing to see such a tremendous growth in a person who earlier wasn't even willing to give away his water bottle, now is prepared to sacrifice his wife.
Spoiled boy now a responsible man caring about his wife's feelings
A matured responsible man taking care of his wife
This is the first time I have seen a character growing from a spoiled, irresponsible boy in pink speedos to a matured responsible married man in UB shirts. What I am waiting for now is to see this matured man turn into a good father.
Sid from a spoiled brat turned to a married responsible man and a good husband and hopefully we get to see him as a good father too.