The long tail keywords are used for specific searches and short tail keywords are used for general purposes,
Take the example of any general-purpose searches like
E.g. marketing — — is the short tail keyword search,
Now take the same search term for specific purposes like
E.g. Digital marketing institute in India — is the long tail keyword
search.
Now!
Why we should use the long tail keyword?
In answering this question I will put a question for you,
Do you fight a battle in which you have more chances of defeat on looking after your ability,
Nobody will fight such a battle,
Similar is the case with the short tail keyword, in that it is very difficult to rank in SERP as it is very tough to overcome from the already ranked page in google with a short tail keyword.
Also, it is a proven fact that long tail keywords work better than short tail keywords.
Just see the below image as a chart of why it is better to use the long tail keyword than the short tail keyword,