long-term investing

Observation from a long-term investor:

In the last three years my portfolio returned roughly 50% in capital appreciation — not including the dividend stream.

What this taught me is something simple:

Most people are not losing money because markets are impossible.

They are losing because they cannot sit still.

Patience is the rarest asset in investing.

Curious to hear from others here:

What has been the hardest part of long-term investing for you?