No matter what you may tell yourself, humans are unable to multitask - do multiple things efficiently at once. What we can do is switch working on one task to working on a different task. And every switch that you make requires mental energy and you only have so much of it every day.

Moreover, it can take up to 30 minutes to fully switch contexts from one task to another. So if you make 16 context switches per day, you effectively do nothing throughout your day. And that's more common than you think.

What to do about it?

1. Prioritize your tasks.

So you always know what's the most important thing to work on and work only on that.

2. Postpone responding to requests.

When urgent things come up - e.g. someone asks for your help, there's an issue at work, etc. determine whether it can wait or it should be handled immediately. If it can wait, then focus on the work you were doing before the interruption.

So you don't interrupt your focus, it's best if you let your teammates know in advance that you respond to their requests within some time frame instead of immediately.

You can also set specific timeframes when you check your emails, messages, etc. E.g. 2-3 times per day - in the morning, noon, and before leaving. Unless there's an incident going on, it's very unlikely that you have to respond to any request immediately.

Also, I would suggest using the no hello policy so you can respond when it fits your timeframe. This alone can make urgent requests non-urgent.