What others have taught, I also teach:
The forceful and violent will not die from natural causes.
This will be my chief doctrine.
This site offers the following interpretation :
The last lines could very well be intended as separate from the preceding ones. It's a simple statement. Those who live violently risk dying the same way. History has shown us countless examples of it.
Here, too, moderation is to recommend [= moderation is recommended]. Lao Tzu repeats that we should avoid any extremes. Although he rarely makes moral judgments on people's life choices, he does confess that he is repelled by brutality, and by the search for personal gain gone wild.
He will come back to it in other chapters, but already here he is quite clear about it. Don't rock the boat, especially not for personal gain. Nature is rich enough to support us all in abundance, if there are not some who forcefully claim much more than their share.
'Those who live violently risk dying the same way' is not, of course, what Lao Tzu (Laozi) actually says in the original or in this translation. But it is perfectly possible that 'A violent man does not die a natural death' functions only to imply that such a man risks - strongly risks - an unnatural death. The statement is to be taken not in its strict linguistic meaning but as what H.P. Grice termed its 'conversational implicature'. In the same way we say, 'Criminals end up in prison'. We know that not all criminals end up in prison but the point is that there is a high probability that they will. They risk emprisonment and this is what 'Criminals end up in prison' indicates. It is a slight over-statement that increases the impact of a valid point; and I think 'A violent man does not die a natural death' is to be taken in the same way.
That is, at least, my interpretation. But other Answers may take a different view. I might add that, as virmaior has pointed out to me, Lao-Tzu (Laozi) is unlikely to have been an actual person. (Compare Homer.)