Difference between Occurs and Happen

OCCURS vs HAPPEN: VERB

To come to pass.
To come about as a consequence; result.
To be the fate; become.
To encounter something by chance.
To come or go casually; make an appearance.
To have the fortune (to be or do something); be in a situation or position (to be or do something).
Used with an infinitive to make polite requests.
To come by chance; to come without previous expectation; to fall out.
To take place; to occur.
To meet with; to fall or light upon.
To make a casual call.
Used with the impersonal subject it and a following clause or infinitive to indicate the occurrence of a usually unexpected or chance event.

Possibly; perhaps.
To occur by chance; occur unexpectedly or unaccountably; in general, to occur; take place.
To chance; be by chance or unexpectedly: as, he happened to be at home.
Fortunate; happy; blessed.
(Santayana)
Meet with
Come into being
Become reality
Come upon, as if by accident

Comes, Occurrence, Affects, Arises, Happens, Go on, Come about, Pass off, Pass, Take place, Hap, Be, Come, Anticipate, Happen

Come about, Pass off, Bechance, Go on, Take place, Hap, Encounter, Chance, Pass, Bump, Hit, Find, Befall, Materialize, Occur

Extends, Unfolds, Arrives, Applies, Goes, Begins, Occurrence, Go on, Come about, Pass, Take place, Hap, Come, Anticipate, Happen

Recur, Unfold, Come, Come about, Go on, Take place, Hap, Encounter, Chance, Pass, Bump, Hit, Find, Materialize, Occur

For each gain indicate how often it occurs.
The defendant will be present when this occurs.
The upset sale usually occurs in early September.
For example, control this behavior when it occurs.
At ECHO this usually occurs in late November.
Family interfering work occurs in the other way.
This always occurs on its own by puberty.
It occurs in two stages: transcription and translation.
This occurs because a trade off occurs when a conservative society allows a business built in a liberal society to interact with its people.
Osteoporosis develops when bone removal occurs too quickly, replacement occurs too slowly, or both.

It basically describes all the horrible things that happen in hell and all the awesome things that happen in heaven.
Make sure it is clear what will happen when the rules are followed and what will happen when they are not.
And if it can happen to Jennifer Love Hewitt, it can happen to you.
Richard Stamp of London had one of the worst things that can happen to a man happen to him, he lost his fucking penis.
Although this used to happen regularly under the Supporting People programme, it does not happen regularly now.
And that again will not happen immediately, but could happen over the next year or so if his conviction is upheld.
That way at least you know what will happen should something similar happen in the future.
Meaning: If you want something to happen, make it happen.
Some want it to happen, some wish it would happen, other make it happen.
Yet assumptions have a major impact on what individuals expect will happen, can happen, or should happen.