Have you ever wondered why the external world can never give us non-stop happiness?
The answer is: The outside world is never constant – there is only one thing constant about the external world, and that is CHANGE.
For example: Maybe you love the new job that you just got, and are finding it enriching and stimulating. But what happens a few years down the line when the job becomes repetitive or your team members change and you do not enjoy the company of the new lot of co-workers? The outside world is always changing – so no lasting, permanent happiness can be found there.
Now, if we want permanent happiness, we have to invest ourselves in what is unchanging and eternal. The soul (ātmā) within is unchanging and eternal. But if we invest ourselves in something that, by its very nature is impermanent, then that is the kind of happiness we will get – short-lived and impermanent happiness.