This can be very embarrassing if you have to give a speech and lose your train of thought due to nervousness or distractions in your surroundings and come to a standstill. External and internal distractions as well as nervousness are the most common causes of this kind of mental breakdown. How do you prevent these distractions so that you don't lose your train of thought?

There are a few strategies that you can learn to avoid being distracted by your own thoughts. In the case of internal distractions such as nervousness or stress, regular practice helps you to concentrate. The beginning of the speech is important, the first two or three minutes must be so solid that you can reel them off in your sleep. The nervous system is most tense immediately before and during the first few sentences of the speech. The pulse quickens, the heart pounds. Once you have made it to the beginning, your body begins to adapt to the role and relax.
The beginning of the speech is also so important because this is when the audience forms their first impression of the speaker and, as we all know, first impressions are crucial. If you make it past the hurdle of the first few sentences, your self-confidence and charisma will increase. This improves contact with the audience.

Some people suffer from external distractions, i.e. they see or hear something in the audience and forget what they have just said and the point they were trying to make. To counter this, it helps to end the sentence undramatically and take a meaningful pause during which you smile at the audience. Take a deep breath until the next point of the speech comes to mind.
To prevent such external distractions, you can do regular meditation exercises at home. Meditation teaches you to concentrate fully on your own inner self and not be distracted by noise.

As a speaker, it's good to understand that not every second of speaking time needs to be filled and the audience is on the speaker's side. The audience is there to be entertained because there is a reason for being at the lectern. You don't have to be perfect, so you don't have to be nervous. It is often the human side of the speaker that makes them likeable to the audience. So if he loses the thread due to a distraction, it often helps to tell the audience exactly that. Not only does the audience understand such things, but most of them would never want to stand at the lectern themselves and admire the speaker for that alone.