Concentration (ˌkänsənˈtrāSH(ə)n məˈkaniks)

How Does Concentration Work

If a spell has the duration of “concentration,” you’re putting a lot of your focus into it. You can end a Concentration effect at any time before the listed duration, if you wish.
Despite your focus, you can still cast magic or attack with a weapon while Concentrating. There are three listed effects in the Basic Rules that end a Concentration effect.

• Casting another concentration spell ends the first concentration spell. You can’t have two going simultaneously.
• If you take damage while concentrating, you must roll a Constitution saving throw (DC 10 or half the damage taken, whichever is higher). Should you fail, you lose concentration. If you take damage from multiple sources, you roll separately… though that’s rare in 5E. How unlucky you must be to get bombarded so much at the same time!
• If you’re incapacitated or instantly die, your concentration ends. That one might be obvious.
  

Does Anything Else Break Concentration?

Your DM can rule that certain other environmental effects cause you to break concentration. For example, if you’re in a whirling hurricane, a DM might say you need to really focus to concentrate, and give you a DC 10 Constitution save every round. Or, if you’re being thrown between two giants while stuck in a barrel, your DM might rule the save is DC 12. It’s up to the situation, really!
Any character with the Mage Slayer feat might force a caster to make a Concentration check, and at disadvantage.
Otherwise, the most common way to stop concentration is with Stuns. Anything that Stuns or knocks you out instantly breaks concentration. If a monster can cause paralysis, that can stop your concentrating too!

Can I Make Concentration Checks Easier?

The most common feat for concentration checks is War Caster. War Caster gives you advantage on Constitution saving throws for spells, on top of other huge benefits. Taking the Resilient feat for Constitution adds proficiency bonus to your Constitution saves; that’s a save most casters don’t get access to!
Select few casting classes have additional ways to help their concentration. Wizards of the Conjuration and War Magic focus have abilities tailored around reducing concentration checks (though I personally prefer War Mage).

Wrapping Up Concentration

Concentration is a mechanic designed to prevent the Caster problem from earlier editions. In those days, Concentration spells took your full Action… but only like, 2 spells had it. They were restrictive but uncommon.
Now, they’re much more common, but much less restrictive! Concentration is used to ensure casters don’t have too many strong spell effects at once, and gives non-casters ways to stop dangerous spells. Know if your next spell has Concentration, because it’s going to change how you fight for a few rounds!

Source: August 21, 2020 Jason Toro
 https://www.nerdsandscoundrels.com/how-does-concentration-work-5e/

Type

Metaphysical, Arcane