A simplified way of saying, "Life goes on". The phrase first came to be in the popular beatles song by the same name, and since then, has became an extremely common phrase in pop and youth culture.
One of the more common scenarios for using "Ob-La-Di-Ob-La-Da"

Exemplified Man #1: "Hey man, what's cracka-lackin?"
Exemplified Man #2: "My boss denied me the f@#$%ng promotion I've been wanting due to my 'repulsive hygiene'..."
Exemplified Man #1: "Well, you could always try using--"
Exemplified Man #2: "Ob-La-Di-Ob-La-Da!"
Exemplified Man #1: "Uhmm... What?"
Exemplified Man #2: "Ob-La-Di-Ob-La-Da... You know! (sings) Ob-La-Di-Ob-La-Da, life goes on, Bra---"
Exemplified Man #1: "Oh, Now I see! You are using 'Ob-La-Di-Ob-La-Da' as slang for 'life goes on'- which, everyone knows are the following lyrics in the popular, yet obnoxious Beatles tune! Such an obviously interpretable phrase should be used more often! I too, am going to begin using this phrase commonly in my speech!"
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A very controversial song by The Beatles detailing the relationship of two lovebirds named Desmond and Molly, from when they first met to when they are happily married. Despite being very well-received, the song is often considered one of the worst songs of the 1960's, and was even declared the worst song of all time in a poll. John and George reportedly hated the song, and several others lambasted it for its "lightheartedness."

In the mid-2010's, a parody of the song, titled "Gotta Love Millennials" was released. The parody, as you can probably infer by the titles, is a musical number making fun of millennials.
Desmond has a barrow in the marketplace
Molly is the singer in a band
Desmond says to Molly, "Girl, I like your face"
And Molly says this as she takes him by the hand:

Ob la di, ob la da, life goes on, brah
La-la, how the life goes on
Ob la di, ob la da, life goes on, brah
La-la, how the life goes on

Desmond takes a trolley to the jeweler's store
Buys a twenty carat golden ring
Takes it back to Molly waiting at the door
And as he gives it to her, she begins to sing

Ob la di, ob la da, life goes on, brah
La-la, how the life goes on
Ob la di, ob la da, life goes on, brah
La-la, how the life goes on

In a couple of years they have built
A home sweet home
With a couple of kids running in the yard
Of Desmond and Molly Jones

Happy ever after in the market place
Desmond lets the children lend a hand
Molly stays at home and does her pretty face
And in the evening she still sings it with the band

Ob la di, ob la da, life goes on, brah
La-la, how the life goes on
Ob la di, ob la da, life goes on, brah
La-la, how the life goes on

In a couple of years they have built
A home sweet home
With a couple of kids running in the yard
Of Desmond and Molly Jones

Happy ever after in the market place
Molly lets the children lend a hand
Desmond stays at home and does his pretty face
And in the evening she's a singer with the band

Ob la di, ob la da, life goes on, brah
La-la, how the life goes on
Ob la di, ob la da, life goes on, brah
La-la, how the life goes on
by Someone who kinda exists November 24, 2021
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sumn drake would say
“la-di-frickin-da“ - dayum! Sumn drake would say
by Airs :) October 19, 2021
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